path: root/contrib/postgres_fdw/deparse.c

/*-------------------------------------------------------------------------
 *
 * deparse.c
 *		  Query deparser for postgres_fdw
 *
 * This file includes functions that examine query WHERE clauses to see
 * whether they're safe to send to the remote server for execution, as
 * well as functions to construct the query text to be sent.  The latter
 * functionality is annoyingly duplicative of ruleutils.c, but there are
 * enough special considerations that it seems best to keep this separate.
 * One saving grace is that we only need deparse logic for node types that
 * we consider safe to send.
 *
 * We assume that the remote session's search_path is exactly "pg_catalog",
 * and thus we need schema-qualify all and only names outside pg_catalog.
 *
 * We do not consider that it is ever safe to send COLLATE expressions to
 * the remote server: it might not have the same collation names we do.
 * (Later we might consider it safe to send COLLATE "C", but even that would
 * fail on old remote servers.)  An expression is considered safe to send
 * only if all operator/function input collations used in it are traceable to
 * Var(s) of the foreign table.  That implies that if the remote server gets
 * a different answer than we do, the foreign table's columns are not marked
 * with collations that match the remote table's columns, which we can
 * consider to be user error.
 *
 * Portions Copyright (c) 2012-2023, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *		  contrib/postgres_fdw/deparse.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_authid.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_opfamily.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_ts_config.h"
#include "catalog/pg_ts_dict.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/plannodes.h"
#include "optimizer/optimizer.h"
#include "optimizer/prep.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
#include "postgres_fdw.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"
#include "utils/typcache.h"
#include "commands/tablecmds.h"

/*
 * Global context for foreign_expr_walker's search of an expression tree.
 */
typedef struct foreign_glob_cxt
{
	PlannerInfo *root;			/* global planner state */
	RelOptInfo *foreignrel;		/* the foreign relation we are planning for */
	Relids		relids;			/* relids of base relations in the underlying
								 * scan */
} foreign_glob_cxt;

/*
 * Local (per-tree-level) context for foreign_expr_walker's search.
 * This is concerned with identifying collations used in the expression.
 */
typedef enum
{
	FDW_COLLATE_NONE,			/* expression is of a noncollatable type, or
								 * it has default collation that is not
								 * traceable to a foreign Var */
	FDW_COLLATE_SAFE,			/* collation derives from a foreign Var */
	FDW_COLLATE_UNSAFE			/* collation is non-default and derives from
								 * something other than a foreign Var */
} FDWCollateState;

typedef struct foreign_loc_cxt
{
	Oid			collation;		/* OID of current collation, if any */
	FDWCollateState state;		/* state of current collation choice */
} foreign_loc_cxt;

/*
 * Context for deparseExpr
 */
typedef struct deparse_expr_cxt
{
	PlannerInfo *root;			/* global planner state */
	RelOptInfo *foreignrel;		/* the foreign relation we are planning for */
	RelOptInfo *scanrel;		/* the underlying scan relation. Same as
								 * foreignrel, when that represents a join or
								 * a base relation. */
	StringInfo	buf;			/* output buffer to append to */
	List	  **params_list;	/* exprs that will become remote Params */
} deparse_expr_cxt;

#define REL_ALIAS_PREFIX	"r"
/* Handy macro to add relation name qualification */
#define ADD_REL_QUALIFIER(buf, varno)	\
		appendStringInfo((buf), "%s%d.", REL_ALIAS_PREFIX, (varno))
#define SUBQUERY_REL_ALIAS_PREFIX	"s"
#define SUBQUERY_COL_ALIAS_PREFIX	"c"

/*
 * Functions to determine whether an expression can be evaluated safely on
 * remote server.
 */
static bool foreign_expr_walker(Node *node,
								foreign_glob_cxt *glob_cxt,
								foreign_loc_cxt *outer_cxt,
								foreign_loc_cxt *case_arg_cxt);
static char *deparse_type_name(Oid type_oid, int32 typemod);

/*
 * Functions to construct string representation of a node tree.
 */
static void deparseTargetList(StringInfo buf,
							  RangeTblEntry *rte,
							  Index rtindex,
							  Relation rel,
							  bool is_returning,
							  Bitmapset *attrs_used,
							  bool qualify_col,
							  List **retrieved_attrs);
static void deparseExplicitTargetList(List *tlist,
									  bool is_returning,
									  List **retrieved_attrs,
									  deparse_expr_cxt *context);
static void deparseSubqueryTargetList(deparse_expr_cxt *context);
static void deparseReturningList(StringInfo buf, RangeTblEntry *rte,
								 Index rtindex, Relation rel,
								 bool trig_after_row,
								 List *withCheckOptionList,
								 List *returningList,
								 List **retrieved_attrs);
static void deparseColumnRef(StringInfo buf, int varno, int varattno,
							 RangeTblEntry *rte, bool qualify_col);
static void deparseRelation(StringInfo buf, Relation rel);
static void deparseExpr(Expr *node, deparse_expr_cxt *context);
static void deparseVar(Var *node, deparse_expr_cxt *context);
static void deparseConst(Const *node, deparse_expr_cxt *context, int showtype);
static void deparseParam(Param *node, deparse_expr_cxt *context);
static void deparseSubscriptingRef(SubscriptingRef *node, deparse_expr_cxt *context);
static void deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context);
static void deparseOpExpr(OpExpr *node, deparse_expr_cxt *context);
static bool isPlainForeignVar(Expr *node, deparse_expr_cxt *context);
static void deparseOperatorName(StringInfo buf, Form_pg_operator opform);
static void deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context);
static void deparseScalarArrayOpExpr(ScalarArrayOpExpr *node,
									 deparse_expr_cxt *context);
static void deparseRelabelType(RelabelType *node, deparse_expr_cxt *context);
static void deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context);
static void deparseNullTest(NullTest *node, deparse_expr_cxt *context);
static void deparseCaseExpr(CaseExpr *node, deparse_expr_cxt *context);
static void deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context);
static void printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
							 deparse_expr_cxt *context);
static void printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
								   deparse_expr_cxt *context);
static void deparseSelectSql(List *tlist, bool is_subquery, List **retrieved_attrs,
							 deparse_expr_cxt *context);
static void deparseLockingClause(deparse_expr_cxt *context);
static void appendOrderByClause(List *pathkeys, bool has_final_sort,
								deparse_expr_cxt *context);
static void appendLimitClause(deparse_expr_cxt *context);
static void appendConditions(List *exprs, deparse_expr_cxt *context);
static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
								  RelOptInfo *foreignrel, bool use_alias,
								  Index ignore_rel, List **ignore_conds,
								  List **params_list);
static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
							   RelOptInfo *foreignrel, bool make_subquery,
							   Index ignore_rel, List **ignore_conds, List **params_list);
static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
static void appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
								deparse_expr_cxt *context);
static void appendAggOrderBy(List *orderList, List *targetList,
							 deparse_expr_cxt *context);
static void appendFunctionName(Oid funcid, deparse_expr_cxt *context);
static Node *deparseSortGroupClause(Index ref, List *tlist, bool force_colno,
									deparse_expr_cxt *context);

/*
 * Helper functions
 */
static bool is_subquery_var(Var *node, RelOptInfo *foreignrel,
							int *relno, int *colno);
static void get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
										  int *relno, int *colno);


/*
 * Examine each qual clause in input_conds, and classify them into two groups,
 * which are returned as two lists:
 *	- remote_conds contains expressions that can be evaluated remotely
 *	- local_conds contains expressions that can't be evaluated remotely
 */
void
classifyConditions(PlannerInfo *root,
				   RelOptInfo *baserel,
				   List *input_conds,
				   List **remote_conds,
				   List **local_conds)
{
	ListCell   *lc;

	*remote_conds = NIL;
	*local_conds = NIL;

	foreach(lc, input_conds)
	{
		RestrictInfo *ri = lfirst_node(RestrictInfo, lc);

		if (is_foreign_expr(root, baserel, ri->clause))
			*remote_conds = lappend(*remote_conds, ri);
		else
			*local_conds = lappend(*local_conds, ri);
	}
}

/*
 * Returns true if given expr is safe to evaluate on the foreign server.
 */
bool
is_foreign_expr(PlannerInfo *root,
				RelOptInfo *baserel,
				Expr *expr)
{
	foreign_glob_cxt glob_cxt;
	foreign_loc_cxt loc_cxt;
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) (baserel->fdw_private);

	/*
	 * Check that the expression consists of nodes that are safe to execute
	 * remotely.
	 */
	glob_cxt.root = root;
	glob_cxt.foreignrel = baserel;

	/*
	 * For an upper relation, use relids from its underneath scan relation,
	 * because the upperrel's own relids currently aren't set to anything
	 * meaningful by the core code.  For other relation, use their own relids.
	 */
	if (IS_UPPER_REL(baserel))
		glob_cxt.relids = fpinfo->outerrel->relids;
	else
		glob_cxt.relids = baserel->relids;
	loc_cxt.collation = InvalidOid;
	loc_cxt.state = FDW_COLLATE_NONE;
	if (!foreign_expr_walker((Node *) expr, &glob_cxt, &loc_cxt, NULL))
		return false;

	/*
	 * If the expression has a valid collation that does not arise from a
	 * foreign var, the expression can not be sent over.
	 */
	if (loc_cxt.state == FDW_COLLATE_UNSAFE)
		return false;

	/*
	 * An expression which includes any mutable functions can't be sent over
	 * because its result is not stable.  For example, sending now() remote
	 * side could cause confusion from clock offsets.  Future versions might
	 * be able to make this choice with more granularity.  (We check this last
	 * because it requires a lot of expensive catalog lookups.)
	 */
	if (contain_mutable_functions((Node *) expr))
		return false;

	/* OK to evaluate on the remote server */
	return true;
}

/*
 * Check if expression is safe to execute remotely, and return true if so.
 *
 * In addition, *outer_cxt is updated with collation information.
 *
 * case_arg_cxt is NULL if this subexpression is not inside a CASE-with-arg.
 * Otherwise, it points to the collation info derived from the arg expression,
 * which must be consulted by any CaseTestExpr.
 *
 * We must check that the expression contains only node types we can deparse,
 * that all types/functions/operators are safe to send (they are "shippable"),
 * and that all collations used in the expression derive from Vars of the
 * foreign table.  Because of the latter, the logic is pretty close to
 * assign_collations_walker() in parse_collate.c, though we can assume here
 * that the given expression is valid.  Note function mutability is not
 * currently considered here.
 */
static bool
foreign_expr_walker(Node *node,
					foreign_glob_cxt *glob_cxt,
					foreign_loc_cxt *outer_cxt,
					foreign_loc_cxt *case_arg_cxt)
{
	bool		check_type = true;
	PgFdwRelationInfo *fpinfo;
	foreign_loc_cxt inner_cxt;
	Oid			collation;
	FDWCollateState state;

	/* Need do nothing for empty subexpressions */
	if (node == NULL)
		return true;

	/* May need server info from baserel's fdw_private struct */
	fpinfo = (PgFdwRelationInfo *) (glob_cxt->foreignrel->fdw_private);

	/* Set up inner_cxt for possible recursion to child nodes */
	inner_cxt.collation = InvalidOid;
	inner_cxt.state = FDW_COLLATE_NONE;

	switch (nodeTag(node))
	{
		case T_Var:
			{
				Var		   *var = (Var *) node;

				/*
				 * If the Var is from the foreign table, we consider its
				 * collation (if any) safe to use.  If it is from another
				 * table, we treat its collation the same way as we would a
				 * Param's collation, ie it's not safe for it to have a
				 * non-default collation.
				 */
				if (bms_is_member(var->varno, glob_cxt->relids) &&
					var->varlevelsup == 0)
				{
					/* Var belongs to foreign table */

					/*
					 * System columns other than ctid should not be sent to
					 * the remote, since we don't make any effort to ensure
					 * that local and remote values match (tableoid, in
					 * particular, almost certainly doesn't match).
					 */
					if (var->varattno < 0 &&
						var->varattno != SelfItemPointerAttributeNumber)
						return false;

					/* Else check the collation */
					collation = var->varcollid;
					state = OidIsValid(collation) ? FDW_COLLATE_SAFE : FDW_COLLATE_NONE;
				}
				else
				{
					/* Var belongs to some other table */
					collation = var->varcollid;
					if (collation == InvalidOid ||
						collation == DEFAULT_COLLATION_OID)
					{
						/*
						 * It's noncollatable, or it's safe to combine with a
						 * collatable foreign Var, so set state to NONE.
						 */
						state = FDW_COLLATE_NONE;
					}
					else
					{
						/*
						 * Do not fail right away, since the Var might appear
						 * in a collation-insensitive context.
						 */
						state = FDW_COLLATE_UNSAFE;
					}
				}
			}
			break;
		case T_Const:
			{
				Const	   *c = (Const *) node;

				/*
				 * Constants of regproc and related types can't be shipped
				 * unless the referenced object is shippable.  But NULL's ok.
				 * (See also the related code in dependency.c.)
				 */
				if (!c->constisnull)
				{
					switch (c->consttype)
					{
						case REGPROCOID:
						case REGPROCEDUREOID:
							if (!is_shippable(DatumGetObjectId(c->constvalue),
											  ProcedureRelationId, fpinfo))
								return false;
							break;
						case REGOPEROID:
						case REGOPERATOROID:
							if (!is_shippable(DatumGetObjectId(c->constvalue),
											  OperatorRelationId, fpinfo))
								return false;
							break;
						case REGCLASSOID:
							if (!is_shippable(DatumGetObjectId(c->constvalue),
											  RelationRelationId, fpinfo))
								return false;
							break;
						case REGTYPEOID:
							if (!is_shippable(DatumGetObjectId(c->constvalue),
											  TypeRelationId, fpinfo))
								return false;
							break;
						case REGCOLLATIONOID:
							if (!is_shippable(DatumGetObjectId(c->constvalue),
											  CollationRelationId, fpinfo))
								return false;
							break;
						case REGCONFIGOID:

							/*
							 * For text search objects only, we weaken the
							 * normal shippability criterion to allow all OIDs
							 * below FirstNormalObjectId.  Without this, none
							 * of the initdb-installed TS configurations would
							 * be shippable, which would be quite annoying.
							 */
							if (DatumGetObjectId(c->constvalue) >= FirstNormalObjectId &&
								!is_shippable(DatumGetObjectId(c->constvalue),
											  TSConfigRelationId, fpinfo))
								return false;
							break;
						case REGDICTIONARYOID:
							if (DatumGetObjectId(c->constvalue) >= FirstNormalObjectId &&
								!is_shippable(DatumGetObjectId(c->constvalue),
											  TSDictionaryRelationId, fpinfo))
								return false;
							break;
						case REGNAMESPACEOID:
							if (!is_shippable(DatumGetObjectId(c->constvalue),
											  NamespaceRelationId, fpinfo))
								return false;
							break;
						case REGROLEOID:
							if (!is_shippable(DatumGetObjectId(c->constvalue),
											  AuthIdRelationId, fpinfo))
								return false;
							break;
					}
				}

				/*
				 * If the constant has nondefault collation, either it's of a
				 * non-builtin type, or it reflects folding of a CollateExpr.
				 * It's unsafe to send to the remote unless it's used in a
				 * non-collation-sensitive context.
				 */
				collation = c->constcollid;
				if (collation == InvalidOid ||
					collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_Param:
			{
				Param	   *p = (Param *) node;

				/*
				 * If it's a MULTIEXPR Param, punt.  We can't tell from here
				 * whether the referenced sublink/subplan contains any remote
				 * Vars; if it does, handling that is too complicated to
				 * consider supporting at present.  Fortunately, MULTIEXPR
				 * Params are not reduced to plain PARAM_EXEC until the end of
				 * planning, so we can easily detect this case.  (Normal
				 * PARAM_EXEC Params are safe to ship because their values
				 * come from somewhere else in the plan tree; but a MULTIEXPR
				 * references a sub-select elsewhere in the same targetlist,
				 * so we'd be on the hook to evaluate it somehow if we wanted
				 * to handle such cases as direct foreign updates.)
				 */
				if (p->paramkind == PARAM_MULTIEXPR)
					return false;

				/*
				 * Collation rule is same as for Consts and non-foreign Vars.
				 */
				collation = p->paramcollid;
				if (collation == InvalidOid ||
					collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_SubscriptingRef:
			{
				SubscriptingRef *sr = (SubscriptingRef *) node;

				/* Assignment should not be in restrictions. */
				if (sr->refassgnexpr != NULL)
					return false;

				/*
				 * Recurse into the remaining subexpressions.  The container
				 * subscripts will not affect collation of the SubscriptingRef
				 * result, so do those first and reset inner_cxt afterwards.
				 */
				if (!foreign_expr_walker((Node *) sr->refupperindexpr,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;
				inner_cxt.collation = InvalidOid;
				inner_cxt.state = FDW_COLLATE_NONE;
				if (!foreign_expr_walker((Node *) sr->reflowerindexpr,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;
				inner_cxt.collation = InvalidOid;
				inner_cxt.state = FDW_COLLATE_NONE;
				if (!foreign_expr_walker((Node *) sr->refexpr,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/*
				 * Container subscripting typically yields same collation as
				 * refexpr's, but in case it doesn't, use same logic as for
				 * function nodes.
				 */
				collation = sr->refcollid;
				if (collation == InvalidOid)
					state = FDW_COLLATE_NONE;
				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
						 collation == inner_cxt.collation)
					state = FDW_COLLATE_SAFE;
				else if (collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_FuncExpr:
			{
				FuncExpr   *fe = (FuncExpr *) node;

				/*
				 * If function used by the expression is not shippable, it
				 * can't be sent to remote because it might have incompatible
				 * semantics on remote side.
				 */
				if (!is_shippable(fe->funcid, ProcedureRelationId, fpinfo))
					return false;

				/*
				 * Recurse to input subexpressions.
				 */
				if (!foreign_expr_walker((Node *) fe->args,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/*
				 * If function's input collation is not derived from a foreign
				 * Var, it can't be sent to remote.
				 */
				if (fe->inputcollid == InvalidOid)
					 /* OK, inputs are all noncollatable */ ;
				else if (inner_cxt.state != FDW_COLLATE_SAFE ||
						 fe->inputcollid != inner_cxt.collation)
					return false;

				/*
				 * Detect whether node is introducing a collation not derived
				 * from a foreign Var.  (If so, we just mark it unsafe for now
				 * rather than immediately returning false, since the parent
				 * node might not care.)
				 */
				collation = fe->funccollid;
				if (collation == InvalidOid)
					state = FDW_COLLATE_NONE;
				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
						 collation == inner_cxt.collation)
					state = FDW_COLLATE_SAFE;
				else if (collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_OpExpr:
		case T_DistinctExpr:	/* struct-equivalent to OpExpr */
			{
				OpExpr	   *oe = (OpExpr *) node;

				/*
				 * Similarly, only shippable operators can be sent to remote.
				 * (If the operator is shippable, we assume its underlying
				 * function is too.)
				 */
				if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
					return false;

				/*
				 * Recurse to input subexpressions.
				 */
				if (!foreign_expr_walker((Node *) oe->args,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/*
				 * If operator's input collation is not derived from a foreign
				 * Var, it can't be sent to remote.
				 */
				if (oe->inputcollid == InvalidOid)
					 /* OK, inputs are all noncollatable */ ;
				else if (inner_cxt.state != FDW_COLLATE_SAFE ||
						 oe->inputcollid != inner_cxt.collation)
					return false;

				/* Result-collation handling is same as for functions */
				collation = oe->opcollid;
				if (collation == InvalidOid)
					state = FDW_COLLATE_NONE;
				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
						 collation == inner_cxt.collation)
					state = FDW_COLLATE_SAFE;
				else if (collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_ScalarArrayOpExpr:
			{
				ScalarArrayOpExpr *oe = (ScalarArrayOpExpr *) node;

				/*
				 * Again, only shippable operators can be sent to remote.
				 */
				if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
					return false;

				/*
				 * Recurse to input subexpressions.
				 */
				if (!foreign_expr_walker((Node *) oe->args,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/*
				 * If operator's input collation is not derived from a foreign
				 * Var, it can't be sent to remote.
				 */
				if (oe->inputcollid == InvalidOid)
					 /* OK, inputs are all noncollatable */ ;
				else if (inner_cxt.state != FDW_COLLATE_SAFE ||
						 oe->inputcollid != inner_cxt.collation)
					return false;

				/* Output is always boolean and so noncollatable. */
				collation = InvalidOid;
				state = FDW_COLLATE_NONE;
			}
			break;
		case T_RelabelType:
			{
				RelabelType *r = (RelabelType *) node;

				/*
				 * Recurse to input subexpression.
				 */
				if (!foreign_expr_walker((Node *) r->arg,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/*
				 * RelabelType must not introduce a collation not derived from
				 * an input foreign Var (same logic as for a real function).
				 */
				collation = r->resultcollid;
				if (collation == InvalidOid)
					state = FDW_COLLATE_NONE;
				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
						 collation == inner_cxt.collation)
					state = FDW_COLLATE_SAFE;
				else if (collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_BoolExpr:
			{
				BoolExpr   *b = (BoolExpr *) node;

				/*
				 * Recurse to input subexpressions.
				 */
				if (!foreign_expr_walker((Node *) b->args,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/* Output is always boolean and so noncollatable. */
				collation = InvalidOid;
				state = FDW_COLLATE_NONE;
			}
			break;
		case T_NullTest:
			{
				NullTest   *nt = (NullTest *) node;

				/*
				 * Recurse to input subexpressions.
				 */
				if (!foreign_expr_walker((Node *) nt->arg,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/* Output is always boolean and so noncollatable. */
				collation = InvalidOid;
				state = FDW_COLLATE_NONE;
			}
			break;
		case T_CaseExpr:
			{
				CaseExpr   *ce = (CaseExpr *) node;
				foreign_loc_cxt arg_cxt;
				foreign_loc_cxt tmp_cxt;
				ListCell   *lc;

				/*
				 * Recurse to CASE's arg expression, if any.  Its collation
				 * has to be saved aside for use while examining CaseTestExprs
				 * within the WHEN expressions.
				 */
				arg_cxt.collation = InvalidOid;
				arg_cxt.state = FDW_COLLATE_NONE;
				if (ce->arg)
				{
					if (!foreign_expr_walker((Node *) ce->arg,
											 glob_cxt, &arg_cxt, case_arg_cxt))
						return false;
				}

				/* Examine the CaseWhen subexpressions. */
				foreach(lc, ce->args)
				{
					CaseWhen   *cw = lfirst_node(CaseWhen, lc);

					if (ce->arg)
					{
						/*
						 * In a CASE-with-arg, the parser should have produced
						 * WHEN clauses of the form "CaseTestExpr = RHS",
						 * possibly with an implicit coercion inserted above
						 * the CaseTestExpr.  However in an expression that's
						 * been through the optimizer, the WHEN clause could
						 * be almost anything (since the equality operator
						 * could have been expanded into an inline function).
						 * In such cases forbid pushdown, because
						 * deparseCaseExpr can't handle it.
						 */
						Node	   *whenExpr = (Node *) cw->expr;
						List	   *opArgs;

						if (!IsA(whenExpr, OpExpr))
							return false;

						opArgs = ((OpExpr *) whenExpr)->args;
						if (list_length(opArgs) != 2 ||
							!IsA(strip_implicit_coercions(linitial(opArgs)),
								 CaseTestExpr))
							return false;
					}

					/*
					 * Recurse to WHEN expression, passing down the arg info.
					 * Its collation doesn't affect the result (really, it
					 * should be boolean and thus not have a collation).
					 */
					tmp_cxt.collation = InvalidOid;
					tmp_cxt.state = FDW_COLLATE_NONE;
					if (!foreign_expr_walker((Node *) cw->expr,
											 glob_cxt, &tmp_cxt, &arg_cxt))
						return false;

					/* Recurse to THEN expression. */
					if (!foreign_expr_walker((Node *) cw->result,
											 glob_cxt, &inner_cxt, case_arg_cxt))
						return false;
				}

				/* Recurse to ELSE expression. */
				if (!foreign_expr_walker((Node *) ce->defresult,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/*
				 * Detect whether node is introducing a collation not derived
				 * from a foreign Var.  (If so, we just mark it unsafe for now
				 * rather than immediately returning false, since the parent
				 * node might not care.)  This is the same as for function
				 * nodes, except that the input collation is derived from only
				 * the THEN and ELSE subexpressions.
				 */
				collation = ce->casecollid;
				if (collation == InvalidOid)
					state = FDW_COLLATE_NONE;
				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
						 collation == inner_cxt.collation)
					state = FDW_COLLATE_SAFE;
				else if (collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_CaseTestExpr:
			{
				CaseTestExpr *c = (CaseTestExpr *) node;

				/* Punt if we seem not to be inside a CASE arg WHEN. */
				if (!case_arg_cxt)
					return false;

				/*
				 * Otherwise, any nondefault collation attached to the
				 * CaseTestExpr node must be derived from foreign Var(s) in
				 * the CASE arg.
				 */
				collation = c->collation;
				if (collation == InvalidOid)
					state = FDW_COLLATE_NONE;
				else if (case_arg_cxt->state == FDW_COLLATE_SAFE &&
						 collation == case_arg_cxt->collation)
					state = FDW_COLLATE_SAFE;
				else if (collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_ArrayExpr:
			{
				ArrayExpr  *a = (ArrayExpr *) node;

				/*
				 * Recurse to input subexpressions.
				 */
				if (!foreign_expr_walker((Node *) a->elements,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/*
				 * ArrayExpr must not introduce a collation not derived from
				 * an input foreign Var (same logic as for a function).
				 */
				collation = a->array_collid;
				if (collation == InvalidOid)
					state = FDW_COLLATE_NONE;
				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
						 collation == inner_cxt.collation)
					state = FDW_COLLATE_SAFE;
				else if (collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		case T_List:
			{
				List	   *l = (List *) node;
				ListCell   *lc;

				/*
				 * Recurse to component subexpressions.
				 */
				foreach(lc, l)
				{
					if (!foreign_expr_walker((Node *) lfirst(lc),
											 glob_cxt, &inner_cxt, case_arg_cxt))
						return false;
				}

				/*
				 * When processing a list, collation state just bubbles up
				 * from the list elements.
				 */
				collation = inner_cxt.collation;
				state = inner_cxt.state;

				/* Don't apply exprType() to the list. */
				check_type = false;
			}
			break;
		case T_Aggref:
			{
				Aggref	   *agg = (Aggref *) node;
				ListCell   *lc;

				/* Not safe to pushdown when not in grouping context */
				if (!IS_UPPER_REL(glob_cxt->foreignrel))
					return false;

				/* Only non-split aggregates are pushable. */
				if (agg->aggsplit != AGGSPLIT_SIMPLE)
					return false;

				/* As usual, it must be shippable. */
				if (!is_shippable(agg->aggfnoid, ProcedureRelationId, fpinfo))
					return false;

				/*
				 * Recurse to input args. aggdirectargs, aggorder and
				 * aggdistinct are all present in args, so no need to check
				 * their shippability explicitly.
				 */
				foreach(lc, agg->args)
				{
					Node	   *n = (Node *) lfirst(lc);

					/* If TargetEntry, extract the expression from it */
					if (IsA(n, TargetEntry))
					{
						TargetEntry *tle = (TargetEntry *) n;

						n = (Node *) tle->expr;
					}

					if (!foreign_expr_walker(n,
											 glob_cxt, &inner_cxt, case_arg_cxt))
						return false;
				}

				/*
				 * For aggorder elements, check whether the sort operator, if
				 * specified, is shippable or not.
				 */
				if (agg->aggorder)
				{
					foreach(lc, agg->aggorder)
					{
						SortGroupClause *srt = (SortGroupClause *) lfirst(lc);
						Oid			sortcoltype;
						TypeCacheEntry *typentry;
						TargetEntry *tle;

						tle = get_sortgroupref_tle(srt->tleSortGroupRef,
												   agg->args);
						sortcoltype = exprType((Node *) tle->expr);
						typentry = lookup_type_cache(sortcoltype,
													 TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
						/* Check shippability of non-default sort operator. */
						if (srt->sortop != typentry->lt_opr &&
							srt->sortop != typentry->gt_opr &&
							!is_shippable(srt->sortop, OperatorRelationId,
										  fpinfo))
							return false;
					}
				}

				/* Check aggregate filter */
				if (!foreign_expr_walker((Node *) agg->aggfilter,
										 glob_cxt, &inner_cxt, case_arg_cxt))
					return false;

				/*
				 * If aggregate's input collation is not derived from a
				 * foreign Var, it can't be sent to remote.
				 */
				if (agg->inputcollid == InvalidOid)
					 /* OK, inputs are all noncollatable */ ;
				else if (inner_cxt.state != FDW_COLLATE_SAFE ||
						 agg->inputcollid != inner_cxt.collation)
					return false;

				/*
				 * Detect whether node is introducing a collation not derived
				 * from a foreign Var.  (If so, we just mark it unsafe for now
				 * rather than immediately returning false, since the parent
				 * node might not care.)
				 */
				collation = agg->aggcollid;
				if (collation == InvalidOid)
					state = FDW_COLLATE_NONE;
				else if (inner_cxt.state == FDW_COLLATE_SAFE &&
						 collation == inner_cxt.collation)
					state = FDW_COLLATE_SAFE;
				else if (collation == DEFAULT_COLLATION_OID)
					state = FDW_COLLATE_NONE;
				else
					state = FDW_COLLATE_UNSAFE;
			}
			break;
		default:

			/*
			 * If it's anything else, assume it's unsafe.  This list can be
			 * expanded later, but don't forget to add deparse support below.
			 */
			return false;
	}

	/*
	 * If result type of given expression is not shippable, it can't be sent
	 * to remote because it might have incompatible semantics on remote side.
	 */
	if (check_type && !is_shippable(exprType(node), TypeRelationId, fpinfo))
		return false;

	/*
	 * Now, merge my collation information into my parent's state.
	 */
	if (state > outer_cxt->state)
	{
		/* Override previous parent state */
		outer_cxt->collation = collation;
		outer_cxt->state = state;
	}
	else if (state == outer_cxt->state)
	{
		/* Merge, or detect error if there's a collation conflict */
		switch (state)
		{
			case FDW_COLLATE_NONE:
				/* Nothing + nothing is still nothing */
				break;
			case FDW_COLLATE_SAFE:
				if (collation != outer_cxt->collation)
				{
					/*
					 * Non-default collation always beats default.
					 */
					if (outer_cxt->collation == DEFAULT_COLLATION_OID)
					{
						/* Override previous parent state */
						outer_cxt->collation = collation;
					}
					else if (collation != DEFAULT_COLLATION_OID)
					{
						/*
						 * Conflict; show state as indeterminate.  We don't
						 * want to "return false" right away, since parent
						 * node might not care about collation.
						 */
						outer_cxt->state = FDW_COLLATE_UNSAFE;
					}
				}
				break;
			case FDW_COLLATE_UNSAFE:
				/* We're still conflicted ... */
				break;
		}
	}

	/* It looks OK */
	return true;
}

/*
 * Returns true if given expr is something we'd have to send the value of
 * to the foreign server.
 *
 * This should return true when the expression is a shippable node that
 * deparseExpr would add to context->params_list.  Note that we don't care
 * if the expression *contains* such a node, only whether one appears at top
 * level.  We need this to detect cases where setrefs.c would recognize a
 * false match between an fdw_exprs item (which came from the params_list)
 * and an entry in fdw_scan_tlist (which we're considering putting the given
 * expression into).
 */
bool
is_foreign_param(PlannerInfo *root,
				 RelOptInfo *baserel,
				 Expr *expr)
{
	if (expr == NULL)
		return false;

	switch (nodeTag(expr))
	{
		case T_Var:
			{
				/* It would have to be sent unless it's a foreign Var */
				Var		   *var = (Var *) expr;
				PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) (baserel->fdw_private);
				Relids		relids;

				if (IS_UPPER_REL(baserel))
					relids = fpinfo->outerrel->relids;
				else
					relids = baserel->relids;

				if (bms_is_member(var->varno, relids) && var->varlevelsup == 0)
					return false;	/* foreign Var, so not a param */
				else
					return true;	/* it'd have to be a param */
				break;
			}
		case T_Param:
			/* Params always have to be sent to the foreign server */
			return true;
		default:
			break;
	}
	return false;
}

/*
 * Returns true if it's safe to push down the sort expression described by
 * 'pathkey' to the foreign server.
 */
bool
is_foreign_pathkey(PlannerInfo *root,
				   RelOptInfo *baserel,
				   PathKey *pathkey)
{
	EquivalenceClass *pathkey_ec = pathkey->pk_eclass;
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) baserel->fdw_private;

	/*
	 * is_foreign_expr would detect volatile expressions as well, but checking
	 * ec_has_volatile here saves some cycles.
	 */
	if (pathkey_ec->ec_has_volatile)
		return false;

	/* can't push down the sort if the pathkey's opfamily is not shippable */
	if (!is_shippable(pathkey->pk_opfamily, OperatorFamilyRelationId, fpinfo))
		return false;

	/* can push if a suitable EC member exists */
	return (find_em_for_rel(root, pathkey_ec, baserel) != NULL);
}

/*
 * Convert type OID + typmod info into a type name we can ship to the remote
 * server.  Someplace else had better have verified that this type name is
 * expected to be known on the remote end.
 *
 * This is almost just format_type_with_typemod(), except that if left to its
 * own devices, that function will make schema-qualification decisions based
 * on the local search_path, which is wrong.  We must schema-qualify all
 * type names that are not in pg_catalog.  We assume here that built-in types
 * are all in pg_catalog and need not be qualified; otherwise, qualify.
 */
static char *
deparse_type_name(Oid type_oid, int32 typemod)
{
	bits16		flags = FORMAT_TYPE_TYPEMOD_GIVEN;

	if (!is_builtin(type_oid))
		flags |= FORMAT_TYPE_FORCE_QUALIFY;

	return format_type_extended(type_oid, typemod, flags);
}

/*
 * Build the targetlist for given relation to be deparsed as SELECT clause.
 *
 * The output targetlist contains the columns that need to be fetched from the
 * foreign server for the given relation.  If foreignrel is an upper relation,
 * then the output targetlist can also contain expressions to be evaluated on
 * foreign server.
 */
List *
build_tlist_to_deparse(RelOptInfo *foreignrel)
{
	List	   *tlist = NIL;
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
	ListCell   *lc;

	/*
	 * For an upper relation, we have already built the target list while
	 * checking shippability, so just return that.
	 */
	if (IS_UPPER_REL(foreignrel))
		return fpinfo->grouped_tlist;

	/*
	 * We require columns specified in foreignrel->reltarget->exprs and those
	 * required for evaluating the local conditions.
	 */
	tlist = add_to_flat_tlist(tlist,
							  pull_var_clause((Node *) foreignrel->reltarget->exprs,
											  PVC_RECURSE_PLACEHOLDERS));
	foreach(lc, fpinfo->local_conds)
	{
		RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);

		tlist = add_to_flat_tlist(tlist,
								  pull_var_clause((Node *) rinfo->clause,
												  PVC_RECURSE_PLACEHOLDERS));
	}

	return tlist;
}

/*
 * Deparse SELECT statement for given relation into buf.
 *
 * tlist contains the list of desired columns to be fetched from foreign server.
 * For a base relation fpinfo->attrs_used is used to construct SELECT clause,
 * hence the tlist is ignored for a base relation.
 *
 * remote_conds is the list of conditions to be deparsed into the WHERE clause
 * (or, in the case of upper relations, into the HAVING clause).
 *
 * If params_list is not NULL, it receives a list of Params and other-relation
 * Vars used in the clauses; these values must be transmitted to the remote
 * server as parameter values.
 *
 * If params_list is NULL, we're generating the query for EXPLAIN purposes,
 * so Params and other-relation Vars should be replaced by dummy values.
 *
 * pathkeys is the list of pathkeys to order the result by.
 *
 * is_subquery is the flag to indicate whether to deparse the specified
 * relation as a subquery.
 *
 * List of columns selected is returned in retrieved_attrs.
 */
void
deparseSelectStmtForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *rel,
						List *tlist, List *remote_conds, List *pathkeys,
						bool has_final_sort, bool has_limit, bool is_subquery,
						List **retrieved_attrs, List **params_list)
{
	deparse_expr_cxt context;
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
	List	   *quals;

	/*
	 * We handle relations for foreign tables, joins between those and upper
	 * relations.
	 */
	Assert(IS_JOIN_REL(rel) || IS_SIMPLE_REL(rel) || IS_UPPER_REL(rel));

	/* Fill portions of context common to upper, join and base relation */
	context.buf = buf;
	context.root = root;
	context.foreignrel = rel;
	context.scanrel = IS_UPPER_REL(rel) ? fpinfo->outerrel : rel;
	context.params_list = params_list;

	/* Construct SELECT clause */
	deparseSelectSql(tlist, is_subquery, retrieved_attrs, &context);

	/*
	 * For upper relations, the WHERE clause is built from the remote
	 * conditions of the underlying scan relation; otherwise, we can use the
	 * supplied list of remote conditions directly.
	 */
	if (IS_UPPER_REL(rel))
	{
		PgFdwRelationInfo *ofpinfo;

		ofpinfo = (PgFdwRelationInfo *) fpinfo->outerrel->fdw_private;
		quals = ofpinfo->remote_conds;
	}
	else
		quals = remote_conds;

	/* Construct FROM and WHERE clauses */
	deparseFromExpr(quals, &context);

	if (IS_UPPER_REL(rel))
	{
		/* Append GROUP BY clause */
		appendGroupByClause(tlist, &context);

		/* Append HAVING clause */
		if (remote_conds)
		{
			appendStringInfoString(buf, " HAVING ");
			appendConditions(remote_conds, &context);
		}
	}

	/* Add ORDER BY clause if we found any useful pathkeys */
	if (pathkeys)
		appendOrderByClause(pathkeys, has_final_sort, &context);

	/* Add LIMIT clause if necessary */
	if (has_limit)
		appendLimitClause(&context);

	/* Add any necessary FOR UPDATE/SHARE. */
	deparseLockingClause(&context);
}

/*
 * Construct a simple SELECT statement that retrieves desired columns
 * of the specified foreign table, and append it to "buf".  The output
 * contains just "SELECT ... ".
 *
 * We also create an integer List of the columns being retrieved, which is
 * returned to *retrieved_attrs, unless we deparse the specified relation
 * as a subquery.
 *
 * tlist is the list of desired columns.  is_subquery is the flag to
 * indicate whether to deparse the specified relation as a subquery.
 * Read prologue of deparseSelectStmtForRel() for details.
 */
static void
deparseSelectSql(List *tlist, bool is_subquery, List **retrieved_attrs,
				 deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	RelOptInfo *foreignrel = context->foreignrel;
	PlannerInfo *root = context->root;
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;

	/*
	 * Construct SELECT list
	 */
	appendStringInfoString(buf, "SELECT ");

	if (is_subquery)
	{
		/*
		 * For a relation that is deparsed as a subquery, emit expressions
		 * specified in the relation's reltarget.  Note that since this is for
		 * the subquery, no need to care about *retrieved_attrs.
		 */
		deparseSubqueryTargetList(context);
	}
	else if (IS_JOIN_REL(foreignrel) || IS_UPPER_REL(foreignrel))
	{
		/*
		 * For a join or upper relation the input tlist gives the list of
		 * columns required to be fetched from the foreign server.
		 */
		deparseExplicitTargetList(tlist, false, retrieved_attrs, context);
	}
	else
	{
		/*
		 * For a base relation fpinfo->attrs_used gives the list of columns
		 * required to be fetched from the foreign server.
		 */
		RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);

		/*
		 * Core code already has some lock on each rel being planned, so we
		 * can use NoLock here.
		 */
		Relation	rel = table_open(rte->relid, NoLock);

		deparseTargetList(buf, rte, foreignrel->relid, rel, false,
						  fpinfo->attrs_used, false, retrieved_attrs);
		table_close(rel, NoLock);
	}
}

/*
 * Construct a FROM clause and, if needed, a WHERE clause, and append those to
 * "buf".
 *
 * quals is the list of clauses to be included in the WHERE clause.
 * (These may or may not include RestrictInfo decoration.)
 */
static void
deparseFromExpr(List *quals, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	RelOptInfo *scanrel = context->scanrel;

	/* For upper relations, scanrel must be either a joinrel or a baserel */
	Assert(!IS_UPPER_REL(context->foreignrel) ||
		   IS_JOIN_REL(scanrel) || IS_SIMPLE_REL(scanrel));

	/* Construct FROM clause */
	appendStringInfoString(buf, " FROM ");
	deparseFromExprForRel(buf, context->root, scanrel,
						  (bms_membership(scanrel->relids) == BMS_MULTIPLE),
						  (Index) 0, NULL, context->params_list);

	/* Construct WHERE clause */
	if (quals != NIL)
	{
		appendStringInfoString(buf, " WHERE ");
		appendConditions(quals, context);
	}
}

/*
 * Emit a target list that retrieves the columns specified in attrs_used.
 * This is used for both SELECT and RETURNING targetlists; the is_returning
 * parameter is true only for a RETURNING targetlist.
 *
 * The tlist text is appended to buf, and we also create an integer List
 * of the columns being retrieved, which is returned to *retrieved_attrs.
 *
 * If qualify_col is true, add relation alias before the column name.
 */
static void
deparseTargetList(StringInfo buf,
				  RangeTblEntry *rte,
				  Index rtindex,
				  Relation rel,
				  bool is_returning,
				  Bitmapset *attrs_used,
				  bool qualify_col,
				  List **retrieved_attrs)
{
	TupleDesc	tupdesc = RelationGetDescr(rel);
	bool		have_wholerow;
	bool		first;
	int			i;

	*retrieved_attrs = NIL;

	/* If there's a whole-row reference, we'll need all the columns. */
	have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
								  attrs_used);

	first = true;
	for (i = 1; i <= tupdesc->natts; i++)
	{
		Form_pg_attribute attr = TupleDescAttr(tupdesc, i - 1);

		/* Ignore dropped attributes. */
		if (attr->attisdropped)
			continue;

		if (have_wholerow ||
			bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
						  attrs_used))
		{
			if (!first)
				appendStringInfoString(buf, ", ");
			else if (is_returning)
				appendStringInfoString(buf, " RETURNING ");
			first = false;

			deparseColumnRef(buf, rtindex, i, rte, qualify_col);

			*retrieved_attrs = lappend_int(*retrieved_attrs, i);
		}
	}

	/*
	 * Add ctid if needed.  We currently don't support retrieving any other
	 * system columns.
	 */
	if (bms_is_member(SelfItemPointerAttributeNumber - FirstLowInvalidHeapAttributeNumber,
					  attrs_used))
	{
		if (!first)
			appendStringInfoString(buf, ", ");
		else if (is_returning)
			appendStringInfoString(buf, " RETURNING ");
		first = false;

		if (qualify_col)
			ADD_REL_QUALIFIER(buf, rtindex);
		appendStringInfoString(buf, "ctid");

		*retrieved_attrs = lappend_int(*retrieved_attrs,
									   SelfItemPointerAttributeNumber);
	}

	/* Don't generate bad syntax if no undropped columns */
	if (first && !is_returning)
		appendStringInfoString(buf, "NULL");
}

/*
 * Deparse the appropriate locking clause (FOR UPDATE or FOR SHARE) for a
 * given relation (context->scanrel).
 */
static void
deparseLockingClause(deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	PlannerInfo *root = context->root;
	RelOptInfo *rel = context->scanrel;
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
	int			relid = -1;

	while ((relid = bms_next_member(rel->relids, relid)) >= 0)
	{
		/*
		 * Ignore relation if it appears in a lower subquery.  Locking clause
		 * for such a relation is included in the subquery if necessary.
		 */
		if (bms_is_member(relid, fpinfo->lower_subquery_rels))
			continue;

		/*
		 * Add FOR UPDATE/SHARE if appropriate.  We apply locking during the
		 * initial row fetch, rather than later on as is done for local
		 * tables. The extra roundtrips involved in trying to duplicate the
		 * local semantics exactly don't seem worthwhile (see also comments
		 * for RowMarkType).
		 *
		 * Note: because we actually run the query as a cursor, this assumes
		 * that DECLARE CURSOR ... FOR UPDATE is supported, which it isn't
		 * before 8.3.
		 */
		if (bms_is_member(relid, root->all_result_relids) &&
			(root->parse->commandType == CMD_UPDATE ||
			 root->parse->commandType == CMD_DELETE))
		{
			/* Relation is UPDATE/DELETE target, so use FOR UPDATE */
			appendStringInfoString(buf, " FOR UPDATE");

			/* Add the relation alias if we are here for a join relation */
			if (IS_JOIN_REL(rel))
				appendStringInfo(buf, " OF %s%d", REL_ALIAS_PREFIX, relid);
		}
		else
		{
			PlanRowMark *rc = get_plan_rowmark(root->rowMarks, relid);

			if (rc)
			{
				/*
				 * Relation is specified as a FOR UPDATE/SHARE target, so
				 * handle that.  (But we could also see LCS_NONE, meaning this
				 * isn't a target relation after all.)
				 *
				 * For now, just ignore any [NO] KEY specification, since (a)
				 * it's not clear what that means for a remote table that we
				 * don't have complete information about, and (b) it wouldn't
				 * work anyway on older remote servers.  Likewise, we don't
				 * worry about NOWAIT.
				 */
				switch (rc->strength)
				{
					case LCS_NONE:
						/* No locking needed */
						break;
					case LCS_FORKEYSHARE:
					case LCS_FORSHARE:
						appendStringInfoString(buf, " FOR SHARE");
						break;
					case LCS_FORNOKEYUPDATE:
					case LCS_FORUPDATE:
						appendStringInfoString(buf, " FOR UPDATE");
						break;
				}

				/* Add the relation alias if we are here for a join relation */
				if (bms_membership(rel->relids) == BMS_MULTIPLE &&
					rc->strength != LCS_NONE)
					appendStringInfo(buf, " OF %s%d", REL_ALIAS_PREFIX, relid);
			}
		}
	}
}

/*
 * Deparse conditions from the provided list and append them to buf.
 *
 * The conditions in the list are assumed to be ANDed. This function is used to
 * deparse WHERE clauses, JOIN .. ON clauses and HAVING clauses.
 *
 * Depending on the caller, the list elements might be either RestrictInfos
 * or bare clauses.
 */
static void
appendConditions(List *exprs, deparse_expr_cxt *context)
{
	int			nestlevel;
	ListCell   *lc;
	bool		is_first = true;
	StringInfo	buf = context->buf;

	/* Make sure any constants in the exprs are printed portably */
	nestlevel = set_transmission_modes();

	foreach(lc, exprs)
	{
		Expr	   *expr = (Expr *) lfirst(lc);

		/* Extract clause from RestrictInfo, if required */
		if (IsA(expr, RestrictInfo))
			expr = ((RestrictInfo *) expr)->clause;

		/* Connect expressions with "AND" and parenthesize each condition. */
		if (!is_first)
			appendStringInfoString(buf, " AND ");

		appendStringInfoChar(buf, '(');
		deparseExpr(expr, context);
		appendStringInfoChar(buf, ')');

		is_first = false;
	}

	reset_transmission_modes(nestlevel);
}

/* Output join name for given join type */
const char *
get_jointype_name(JoinType jointype)
{
	switch (jointype)
	{
		case JOIN_INNER:
			return "INNER";

		case JOIN_LEFT:
			return "LEFT";

		case JOIN_RIGHT:
			return "RIGHT";

		case JOIN_FULL:
			return "FULL";

		default:
			/* Shouldn't come here, but protect from buggy code. */
			elog(ERROR, "unsupported join type %d", jointype);
	}

	/* Keep compiler happy */
	return NULL;
}

/*
 * Deparse given targetlist and append it to context->buf.
 *
 * tlist is list of TargetEntry's which in turn contain Var nodes.
 *
 * retrieved_attrs is the list of continuously increasing integers starting
 * from 1. It has same number of entries as tlist.
 *
 * This is used for both SELECT and RETURNING targetlists; the is_returning
 * parameter is true only for a RETURNING targetlist.
 */
static void
deparseExplicitTargetList(List *tlist,
						  bool is_returning,
						  List **retrieved_attrs,
						  deparse_expr_cxt *context)
{
	ListCell   *lc;
	StringInfo	buf = context->buf;
	int			i = 0;

	*retrieved_attrs = NIL;

	foreach(lc, tlist)
	{
		TargetEntry *tle = lfirst_node(TargetEntry, lc);

		if (i > 0)
			appendStringInfoString(buf, ", ");
		else if (is_returning)
			appendStringInfoString(buf, " RETURNING ");

		deparseExpr((Expr *) tle->expr, context);

		*retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
		i++;
	}

	if (i == 0 && !is_returning)
		appendStringInfoString(buf, "NULL");
}

/*
 * Emit expressions specified in the given relation's reltarget.
 *
 * This is used for deparsing the given relation as a subquery.
 */
static void
deparseSubqueryTargetList(deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	RelOptInfo *foreignrel = context->foreignrel;
	bool		first;
	ListCell   *lc;

	/* Should only be called in these cases. */
	Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

	first = true;
	foreach(lc, foreignrel->reltarget->exprs)
	{
		Node	   *node = (Node *) lfirst(lc);

		if (!first)
			appendStringInfoString(buf, ", ");
		first = false;

		deparseExpr((Expr *) node, context);
	}

	/* Don't generate bad syntax if no expressions */
	if (first)
		appendStringInfoString(buf, "NULL");
}

/*
 * Construct FROM clause for given relation
 *
 * The function constructs ... JOIN ... ON ... for join relation. For a base
 * relation it just returns schema-qualified tablename, with the appropriate
 * alias if so requested.
 *
 * 'ignore_rel' is either zero or the RT index of a target relation.  In the
 * latter case the function constructs FROM clause of UPDATE or USING clause
 * of DELETE; it deparses the join relation as if the relation never contained
 * the target relation, and creates a List of conditions to be deparsed into
 * the top-level WHERE clause, which is returned to *ignore_conds.
 */
static void
deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
					  bool use_alias, Index ignore_rel, List **ignore_conds,
					  List **params_list)
{
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;

	if (IS_JOIN_REL(foreignrel))
	{
		StringInfoData join_sql_o;
		StringInfoData join_sql_i;
		RelOptInfo *outerrel = fpinfo->outerrel;
		RelOptInfo *innerrel = fpinfo->innerrel;
		bool		outerrel_is_target = false;
		bool		innerrel_is_target = false;

		if (ignore_rel > 0 && bms_is_member(ignore_rel, foreignrel->relids))
		{
			/*
			 * If this is an inner join, add joinclauses to *ignore_conds and
			 * set it to empty so that those can be deparsed into the WHERE
			 * clause.  Note that since the target relation can never be
			 * within the nullable side of an outer join, those could safely
			 * be pulled up into the WHERE clause (see foreign_join_ok()).
			 * Note also that since the target relation is only inner-joined
			 * to any other relation in the query, all conditions in the join
			 * tree mentioning the target relation could be deparsed into the
			 * WHERE clause by doing this recursively.
			 */
			if (fpinfo->jointype == JOIN_INNER)
			{
				*ignore_conds = list_concat(*ignore_conds,
											fpinfo->joinclauses);
				fpinfo->joinclauses = NIL;
			}

			/*
			 * Check if either of the input relations is the target relation.
			 */
			if (outerrel->relid == ignore_rel)
				outerrel_is_target = true;
			else if (innerrel->relid == ignore_rel)
				innerrel_is_target = true;
		}

		/* Deparse outer relation if not the target relation. */
		if (!outerrel_is_target)
		{
			initStringInfo(&join_sql_o);
			deparseRangeTblRef(&join_sql_o, root, outerrel,
							   fpinfo->make_outerrel_subquery,
							   ignore_rel, ignore_conds, params_list);

			/*
			 * If inner relation is the target relation, skip deparsing it.
			 * Note that since the join of the target relation with any other
			 * relation in the query is an inner join and can never be within
			 * the nullable side of an outer join, the join could be
			 * interchanged with higher-level joins (cf. identity 1 on outer
			 * join reordering shown in src/backend/optimizer/README), which
			 * means it's safe to skip the target-relation deparsing here.
			 */
			if (innerrel_is_target)
			{
				Assert(fpinfo->jointype == JOIN_INNER);
				Assert(fpinfo->joinclauses == NIL);
				appendBinaryStringInfo(buf, join_sql_o.data, join_sql_o.len);
				return;
			}
		}

		/* Deparse inner relation if not the target relation. */
		if (!innerrel_is_target)
		{
			initStringInfo(&join_sql_i);
			deparseRangeTblRef(&join_sql_i, root, innerrel,
							   fpinfo->make_innerrel_subquery,
							   ignore_rel, ignore_conds, params_list);

			/*
			 * If outer relation is the target relation, skip deparsing it.
			 * See the above note about safety.
			 */
			if (outerrel_is_target)
			{
				Assert(fpinfo->jointype == JOIN_INNER);
				Assert(fpinfo->joinclauses == NIL);
				appendBinaryStringInfo(buf, join_sql_i.data, join_sql_i.len);
				return;
			}
		}

		/* Neither of the relations is the target relation. */
		Assert(!outerrel_is_target && !innerrel_is_target);

		/*
		 * For a join relation FROM clause entry is deparsed as
		 *
		 * ((outer relation) <join type> (inner relation) ON (joinclauses))
		 */
		appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
						 get_jointype_name(fpinfo->jointype), join_sql_i.data);

		/* Append join clause; (TRUE) if no join clause */
		if (fpinfo->joinclauses)
		{
			deparse_expr_cxt context;

			context.buf = buf;
			context.foreignrel = foreignrel;
			context.scanrel = foreignrel;
			context.root = root;
			context.params_list = params_list;

			appendStringInfoChar(buf, '(');
			appendConditions(fpinfo->joinclauses, &context);
			appendStringInfoChar(buf, ')');
		}
		else
			appendStringInfoString(buf, "(TRUE)");

		/* End the FROM clause entry. */
		appendStringInfoChar(buf, ')');
	}
	else
	{
		RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);

		/*
		 * Core code already has some lock on each rel being planned, so we
		 * can use NoLock here.
		 */
		Relation	rel = table_open(rte->relid, NoLock);

		deparseRelation(buf, rel);

		/*
		 * Add a unique alias to avoid any conflict in relation names due to
		 * pulled up subqueries in the query being built for a pushed down
		 * join.
		 */
		if (use_alias)
			appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, foreignrel->relid);

		table_close(rel, NoLock);
	}
}

/*
 * Append FROM clause entry for the given relation into buf.
 */
static void
deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
				   bool make_subquery, Index ignore_rel, List **ignore_conds,
				   List **params_list)
{
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;

	/* Should only be called in these cases. */
	Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

	Assert(fpinfo->local_conds == NIL);

	/* If make_subquery is true, deparse the relation as a subquery. */
	if (make_subquery)
	{
		List	   *retrieved_attrs;
		int			ncols;

		/*
		 * The given relation shouldn't contain the target relation, because
		 * this should only happen for input relations for a full join, and
		 * such relations can never contain an UPDATE/DELETE target.
		 */
		Assert(ignore_rel == 0 ||
			   !bms_is_member(ignore_rel, foreignrel->relids));

		/* Deparse the subquery representing the relation. */
		appendStringInfoChar(buf, '(');
		deparseSelectStmtForRel(buf, root, foreignrel, NIL,
								fpinfo->remote_conds, NIL,
								false, false, true,
								&retrieved_attrs, params_list);
		appendStringInfoChar(buf, ')');

		/* Append the relation alias. */
		appendStringInfo(buf, " %s%d", SUBQUERY_REL_ALIAS_PREFIX,
						 fpinfo->relation_index);

		/*
		 * Append the column aliases if needed.  Note that the subquery emits
		 * expressions specified in the relation's reltarget (see
		 * deparseSubqueryTargetList).
		 */
		ncols = list_length(foreignrel->reltarget->exprs);
		if (ncols > 0)
		{
			int			i;

			appendStringInfoChar(buf, '(');
			for (i = 1; i <= ncols; i++)
			{
				if (i > 1)
					appendStringInfoString(buf, ", ");

				appendStringInfo(buf, "%s%d", SUBQUERY_COL_ALIAS_PREFIX, i);
			}
			appendStringInfoChar(buf, ')');
		}
	}
	else
		deparseFromExprForRel(buf, root, foreignrel, true, ignore_rel,
							  ignore_conds, params_list);
}

/*
 * deparse remote INSERT statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by WITH CHECK OPTION or RETURNING (if any),
 * which is returned to *retrieved_attrs.
 *
 * This also stores end position of the VALUES clause, so that we can rebuild
 * an INSERT for a batch of rows later.
 */
void
deparseInsertSql(StringInfo buf, RangeTblEntry *rte,
				 Index rtindex, Relation rel,
				 List *targetAttrs, bool doNothing,
				 List *withCheckOptionList, List *returningList,
				 List **retrieved_attrs, int *values_end_len)
{
	TupleDesc	tupdesc = RelationGetDescr(rel);
	AttrNumber	pindex;
	bool		first;
	ListCell   *lc;

	appendStringInfoString(buf, "INSERT INTO ");
	deparseRelation(buf, rel);

	if (targetAttrs)
	{
		appendStringInfoChar(buf, '(');

		first = true;
		foreach(lc, targetAttrs)
		{
			int			attnum = lfirst_int(lc);

			if (!first)
				appendStringInfoString(buf, ", ");
			first = false;

			deparseColumnRef(buf, rtindex, attnum, rte, false);
		}

		appendStringInfoString(buf, ") VALUES (");

		pindex = 1;
		first = true;
		foreach(lc, targetAttrs)
		{
			int			attnum = lfirst_int(lc);
			Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);

			if (!first)
				appendStringInfoString(buf, ", ");
			first = false;

			if (attr->attgenerated)
				appendStringInfoString(buf, "DEFAULT");
			else
			{
				appendStringInfo(buf, "$%d", pindex);
				pindex++;
			}
		}

		appendStringInfoChar(buf, ')');
	}
	else
		appendStringInfoString(buf, " DEFAULT VALUES");
	*values_end_len = buf->len;

	if (doNothing)
		appendStringInfoString(buf, " ON CONFLICT DO NOTHING");

	deparseReturningList(buf, rte, rtindex, rel,
						 rel->trigdesc && rel->trigdesc->trig_insert_after_row,
						 withCheckOptionList, returningList, retrieved_attrs);
}

/*
 * rebuild remote INSERT statement
 *
 * Provided a number of rows in a batch, builds INSERT statement with the
 * right number of parameters.
 */
void
rebuildInsertSql(StringInfo buf, Relation rel,
				 char *orig_query, List *target_attrs,
				 int values_end_len, int num_params,
				 int num_rows)
{
	TupleDesc	tupdesc = RelationGetDescr(rel);
	int			i;
	int			pindex;
	bool		first;
	ListCell   *lc;

	/* Make sure the values_end_len is sensible */
	Assert((values_end_len > 0) && (values_end_len <= strlen(orig_query)));

	/* Copy up to the end of the first record from the original query */
	appendBinaryStringInfo(buf, orig_query, values_end_len);

	/*
	 * Add records to VALUES clause (we already have parameters for the first
	 * row, so start at the right offset).
	 */
	pindex = num_params + 1;
	for (i = 0; i < num_rows; i++)
	{
		appendStringInfoString(buf, ", (");

		first = true;
		foreach(lc, target_attrs)
		{
			int			attnum = lfirst_int(lc);
			Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);

			if (!first)
				appendStringInfoString(buf, ", ");
			first = false;

			if (attr->attgenerated)
				appendStringInfoString(buf, "DEFAULT");
			else
			{
				appendStringInfo(buf, "$%d", pindex);
				pindex++;
			}
		}

		appendStringInfoChar(buf, ')');
	}

	/* Copy stuff after VALUES clause from the original query */
	appendStringInfoString(buf, orig_query + values_end_len);
}

/*
 * deparse remote UPDATE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by WITH CHECK OPTION or RETURNING (if any),
 * which is returned to *retrieved_attrs.
 */
void
deparseUpdateSql(StringInfo buf, RangeTblEntry *rte,
				 Index rtindex, Relation rel,
				 List *targetAttrs,
				 List *withCheckOptionList, List *returningList,
				 List **retrieved_attrs)
{
	TupleDesc	tupdesc = RelationGetDescr(rel);
	AttrNumber	pindex;
	bool		first;
	ListCell   *lc;

	appendStringInfoString(buf, "UPDATE ");
	deparseRelation(buf, rel);
	appendStringInfoString(buf, " SET ");

	pindex = 2;					/* ctid is always the first param */
	first = true;
	foreach(lc, targetAttrs)
	{
		int			attnum = lfirst_int(lc);
		Form_pg_attribute attr = TupleDescAttr(tupdesc, attnum - 1);

		if (!first)
			appendStringInfoString(buf, ", ");
		first = false;

		deparseColumnRef(buf, rtindex, attnum, rte, false);
		if (attr->attgenerated)
			appendStringInfoString(buf, " = DEFAULT");
		else
		{
			appendStringInfo(buf, " = $%d", pindex);
			pindex++;
		}
	}
	appendStringInfoString(buf, " WHERE ctid = $1");

	deparseReturningList(buf, rte, rtindex, rel,
						 rel->trigdesc && rel->trigdesc->trig_update_after_row,
						 withCheckOptionList, returningList, retrieved_attrs);
}

/*
 * deparse remote UPDATE statement
 *
 * 'buf' is the output buffer to append the statement to
 * 'rtindex' is the RT index of the associated target relation
 * 'rel' is the relation descriptor for the target relation
 * 'foreignrel' is the RelOptInfo for the target relation or the join relation
 *		containing all base relations in the query
 * 'targetlist' is the tlist of the underlying foreign-scan plan node
 *		(note that this only contains new-value expressions and junk attrs)
 * 'targetAttrs' is the target columns of the UPDATE
 * 'remote_conds' is the qual clauses that must be evaluated remotely
 * '*params_list' is an output list of exprs that will become remote Params
 * 'returningList' is the RETURNING targetlist
 * '*retrieved_attrs' is an output list of integers of columns being retrieved
 *		by RETURNING (if any)
 */
void
deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
					   Index rtindex, Relation rel,
					   RelOptInfo *foreignrel,
					   List *targetlist,
					   List *targetAttrs,
					   List *remote_conds,
					   List **params_list,
					   List *returningList,
					   List **retrieved_attrs)
{
	deparse_expr_cxt context;
	int			nestlevel;
	bool		first;
	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
	ListCell   *lc,
			   *lc2;

	/* Set up context struct for recursion */
	context.root = root;
	context.foreignrel = foreignrel;
	context.scanrel = foreignrel;
	context.buf = buf;
	context.params_list = params_list;

	appendStringInfoString(buf, "UPDATE ");
	deparseRelation(buf, rel);
	if (foreignrel->reloptkind == RELOPT_JOINREL)
		appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, rtindex);
	appendStringInfoString(buf, " SET ");

	/* Make sure any constants in the exprs are printed portably */
	nestlevel = set_transmission_modes();

	first = true;
	forboth(lc, targetlist, lc2, targetAttrs)
	{
		TargetEntry *tle = lfirst_node(TargetEntry, lc);
		int			attnum = lfirst_int(lc2);

		/* update's new-value expressions shouldn't be resjunk */
		Assert(!tle->resjunk);

		if (!first)
			appendStringInfoString(buf, ", ");
		first = false;

		deparseColumnRef(buf, rtindex, attnum, rte, false);
		appendStringInfoString(buf, " = ");
		deparseExpr((Expr *) tle->expr, &context);
	}

	reset_transmission_modes(nestlevel);

	if (foreignrel->reloptkind == RELOPT_JOINREL)
	{
		List	   *ignore_conds = NIL;

		appendStringInfoString(buf, " FROM ");
		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
							  &ignore_conds, params_list);
		remote_conds = list_concat(remote_conds, ignore_conds);
	}

	if (remote_conds)
	{
		appendStringInfoString(buf, " WHERE ");
		appendConditions(remote_conds, &context);
	}

	if (foreignrel->reloptkind == RELOPT_JOINREL)
		deparseExplicitTargetList(returningList, true, retrieved_attrs,
								  &context);
	else
		deparseReturningList(buf, rte, rtindex, rel, false,
							 NIL, returningList, retrieved_attrs);
}

/*
 * deparse remote DELETE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseDeleteSql(StringInfo buf, RangeTblEntry *rte,
				 Index rtindex, Relation rel,
				 List *returningList,
				 List **retrieved_attrs)
{
	appendStringInfoString(buf, "DELETE FROM ");
	deparseRelation(buf, rel);
	appendStringInfoString(buf, " WHERE ctid = $1");

	deparseReturningList(buf, rte, rtindex, rel,
						 rel->trigdesc && rel->trigdesc->trig_delete_after_row,
						 NIL, returningList, retrieved_attrs);
}

/*
 * deparse remote DELETE statement
 *
 * 'buf' is the output buffer to append the statement to
 * 'rtindex' is the RT index of the associated target relation
 * 'rel' is the relation descriptor for the target relation
 * 'foreignrel' is the RelOptInfo for the target relation or the join relation
 *		containing all base relations in the query
 * 'remote_conds' is the qual clauses that must be evaluated remotely
 * '*params_list' is an output list of exprs that will become remote Params
 * 'returningList' is the RETURNING targetlist
 * '*retrieved_attrs' is an output list of integers of columns being retrieved
 *		by RETURNING (if any)
 */
void
deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
					   Index rtindex, Relation rel,
					   RelOptInfo *foreignrel,
					   List *remote_conds,
					   List **params_list,
					   List *returningList,
					   List **retrieved_attrs)
{
	deparse_expr_cxt context;

	/* Set up context struct for recursion */
	context.root = root;
	context.foreignrel = foreignrel;
	context.scanrel = foreignrel;
	context.buf = buf;
	context.params_list = params_list;

	appendStringInfoString(buf, "DELETE FROM ");
	deparseRelation(buf, rel);
	if (foreignrel->reloptkind == RELOPT_JOINREL)
		appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, rtindex);

	if (foreignrel->reloptkind == RELOPT_JOINREL)
	{
		List	   *ignore_conds = NIL;

		appendStringInfoString(buf, " USING ");
		deparseFromExprForRel(buf, root, foreignrel, true, rtindex,
							  &ignore_conds, params_list);
		remote_conds = list_concat(remote_conds, ignore_conds);
	}

	if (remote_conds)
	{
		appendStringInfoString(buf, " WHERE ");
		appendConditions(remote_conds, &context);
	}

	if (foreignrel->reloptkind == RELOPT_JOINREL)
		deparseExplicitTargetList(returningList, true, retrieved_attrs,
								  &context);
	else
		deparseReturningList(buf, planner_rt_fetch(rtindex, root),
							 rtindex, rel, false,
							 NIL, returningList, retrieved_attrs);
}

/*
 * Add a RETURNING clause, if needed, to an INSERT/UPDATE/DELETE.
 */
static void
deparseReturningList(StringInfo buf, RangeTblEntry *rte,
					 Index rtindex, Relation rel,
					 bool trig_after_row,
					 List *withCheckOptionList,
					 List *returningList,
					 List **retrieved_attrs)
{
	Bitmapset  *attrs_used = NULL;

	if (trig_after_row)
	{
		/* whole-row reference acquires all non-system columns */
		attrs_used =
			bms_make_singleton(0 - FirstLowInvalidHeapAttributeNumber);
	}

	if (withCheckOptionList != NIL)
	{
		/*
		 * We need the attrs, non-system and system, mentioned in the local
		 * query's WITH CHECK OPTION list.
		 *
		 * Note: we do this to ensure that WCO constraints will be evaluated
		 * on the data actually inserted/updated on the remote side, which
		 * might differ from the data supplied by the core code, for example
		 * as a result of remote triggers.
		 */
		pull_varattnos((Node *) withCheckOptionList, rtindex,
					   &attrs_used);
	}

	if (returningList != NIL)
	{
		/*
		 * We need the attrs, non-system and system, mentioned in the local
		 * query's RETURNING list.
		 */
		pull_varattnos((Node *) returningList, rtindex,
					   &attrs_used);
	}

	if (attrs_used != NULL)
		deparseTargetList(buf, rte, rtindex, rel, true, attrs_used, false,
						  retrieved_attrs);
	else
		*retrieved_attrs = NIL;
}

/*
 * Construct SELECT statement to acquire size in blocks of given relation.
 *
 * Note: we use local definition of block size, not remote definition.
 * This is perhaps debatable.
 *
 * Note: pg_relation_size() exists in 8.1 and later.
 */
void
deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
{
	StringInfoData relname;

	/* We'll need the remote relation name as a literal. */
	initStringInfo(&relname);
	deparseRelation(&relname, rel);

	appendStringInfoString(buf, "SELECT pg_catalog.pg_relation_size(");
	deparseStringLiteral(buf, relname.data);
	appendStringInfo(buf, "::pg_catalog.regclass) / %d", BLCKSZ);
}

/*
 * Construct SELECT statement to acquire the number of rows and the relkind of
 * a relation.
 *
 * Note: we just return the remote server's reltuples value, which might
 * be off a good deal, but it doesn't seem worth working harder.  See
 * comments in postgresAcquireSampleRowsFunc.
 */
void
deparseAnalyzeInfoSql(StringInfo buf, Relation rel)
{
	StringInfoData relname;

	/* We'll need the remote relation name as a literal. */
	initStringInfo(&relname);
	deparseRelation(&relname, rel);

	appendStringInfoString(buf, "SELECT reltuples, relkind FROM pg_catalog.pg_class WHERE oid = ");
	deparseStringLiteral(buf, relname.data);
	appendStringInfoString(buf, "::pg_catalog.regclass");
}

/*
 * Construct SELECT statement to acquire sample rows of given relation.
 *
 * SELECT command is appended to buf, and list of columns retrieved
 * is returned to *retrieved_attrs.
 *
 * We only support sampling methods we can decide based on server version.
 * Allowing custom TSM modules (like tsm_system_rows) might be useful, but it
 * would require detecting which extensions are installed, to allow automatic
 * fall-back. Moreover, the methods may use different parameters like number
 * of rows (and not sampling rate). So we leave this for future improvements.
 *
 * Using random() to sample rows on the remote server has the advantage that
 * this works on all PostgreSQL versions (unlike TABLESAMPLE), and that it
 * does the sampling on the remote side (without transferring everything and
 * then discarding most rows).
 *
 * The disadvantage is that we still have to read all rows and evaluate the
 * random(), while TABLESAMPLE (at least with the "system" method) may skip.
 * It's not that different from the "bernoulli" method, though.
 *
 * We could also do "ORDER BY random() LIMIT x", which would always pick
 * the expected number of rows, but it requires sorting so it may be much
 * more expensive (particularly on large tables, which is what the
 * remote sampling is meant to improve).
 */
void
deparseAnalyzeSql(StringInfo buf, Relation rel,
				  PgFdwSamplingMethod sample_method, double sample_frac,
				  List **retrieved_attrs)
{
	Oid			relid = RelationGetRelid(rel);
	TupleDesc	tupdesc = RelationGetDescr(rel);
	int			i;
	char	   *colname;
	List	   *options;
	ListCell   *lc;
	bool		first = true;

	*retrieved_attrs = NIL;

	appendStringInfoString(buf, "SELECT ");
	for (i = 0; i < tupdesc->natts; i++)
	{
		/* Ignore dropped columns. */
		if (TupleDescAttr(tupdesc, i)->attisdropped)
			continue;

		if (!first)
			appendStringInfoString(buf, ", ");
		first = false;

		/* Use attribute name or column_name option. */
		colname = NameStr(TupleDescAttr(tupdesc, i)->attname);
		options = GetForeignColumnOptions(relid, i + 1);

		foreach(lc, options)
		{
			DefElem    *def = (DefElem *) lfirst(lc);

			if (strcmp(def->defname, "column_name") == 0)
			{
				colname = defGetString(def);
				break;
			}
		}

		appendStringInfoString(buf, quote_identifier(colname));

		*retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
	}

	/* Don't generate bad syntax for zero-column relation. */
	if (first)
		appendStringInfoString(buf, "NULL");

	/*
	 * Construct FROM clause, and perhaps WHERE clause too, depending on the
	 * selected sampling method.
	 */
	appendStringInfoString(buf, " FROM ");
	deparseRelation(buf, rel);

	switch (sample_method)
	{
		case ANALYZE_SAMPLE_OFF:
			/* nothing to do here */
			break;

		case ANALYZE_SAMPLE_RANDOM:
			appendStringInfo(buf, " WHERE pg_catalog.random() < %f", sample_frac);
			break;

		case ANALYZE_SAMPLE_SYSTEM:
			appendStringInfo(buf, " TABLESAMPLE SYSTEM(%f)", (100.0 * sample_frac));
			break;

		case ANALYZE_SAMPLE_BERNOULLI:
			appendStringInfo(buf, " TABLESAMPLE BERNOULLI(%f)", (100.0 * sample_frac));
			break;

		case ANALYZE_SAMPLE_AUTO:
			/* should have been resolved into actual method */
			elog(ERROR, "unexpected sampling method");
			break;
	}
}

/*
 * Construct a simple "TRUNCATE rel" statement
 */
void
deparseTruncateSql(StringInfo buf,
				   List *rels,
				   DropBehavior behavior,
				   bool restart_seqs)
{
	ListCell   *cell;

	appendStringInfoString(buf, "TRUNCATE ");

	foreach(cell, rels)
	{
		Relation	rel = lfirst(cell);

		if (cell != list_head(rels))
			appendStringInfoString(buf, ", ");

		deparseRelation(buf, rel);
	}

	appendStringInfo(buf, " %s IDENTITY",
					 restart_seqs ? "RESTART" : "CONTINUE");

	if (behavior == DROP_RESTRICT)
		appendStringInfoString(buf, " RESTRICT");
	else if (behavior == DROP_CASCADE)
		appendStringInfoString(buf, " CASCADE");
}

/*
 * Construct name to use for given column, and emit it into buf.
 * If it has a column_name FDW option, use that instead of attribute name.
 *
 * If qualify_col is true, qualify column name with the alias of relation.
 */
static void
deparseColumnRef(StringInfo buf, int varno, int varattno, RangeTblEntry *rte,
				 bool qualify_col)
{
	/* We support fetching the remote side's CTID and OID. */
	if (varattno == SelfItemPointerAttributeNumber)
	{
		if (qualify_col)
			ADD_REL_QUALIFIER(buf, varno);
		appendStringInfoString(buf, "ctid");
	}
	else if (varattno < 0)
	{
		/*
		 * All other system attributes are fetched as 0, except for table OID,
		 * which is fetched as the local table OID.  However, we must be
		 * careful; the table could be beneath an outer join, in which case it
		 * must go to NULL whenever the rest of the row does.
		 */
		Oid			fetchval = 0;

		if (varattno == TableOidAttributeNumber)
			fetchval = rte->relid;

		if (qualify_col)
		{
			appendStringInfoString(buf, "CASE WHEN (");
			ADD_REL_QUALIFIER(buf, varno);
			appendStringInfo(buf, "*)::text IS NOT NULL THEN %u END", fetchval);
		}
		else
			appendStringInfo(buf, "%u", fetchval);
	}
	else if (varattno == 0)
	{
		/* Whole row reference */
		Relation	rel;
		Bitmapset  *attrs_used;

		/* Required only to be passed down to deparseTargetList(). */
		List	   *retrieved_attrs;

		/*
		 * The lock on the relation will be held by upper callers, so it's
		 * fine to open it with no lock here.
		 */
		rel = table_open(rte->relid, NoLock);

		/*
		 * The local name of the foreign table can not be recognized by the
		 * foreign server and the table it references on foreign server might
		 * have different column ordering or different columns than those
		 * declared locally. Hence we have to deparse whole-row reference as
		 * ROW(columns referenced locally). Construct this by deparsing a
		 * "whole row" attribute.
		 */
		attrs_used = bms_add_member(NULL,
									0 - FirstLowInvalidHeapAttributeNumber);

		/*
		 * In case the whole-row reference is under an outer join then it has
		 * to go NULL whenever the rest of the row goes NULL. Deparsing a join
		 * query would always involve multiple relations, thus qualify_col
		 * would be true.
		 */
		if (qualify_col)
		{
			appendStringInfoString(buf, "CASE WHEN (");
			ADD_REL_QUALIFIER(buf, varno);
			appendStringInfoString(buf, "*)::text IS NOT NULL THEN ");
		}

		appendStringInfoString(buf, "ROW(");
		deparseTargetList(buf, rte, varno, rel, false, attrs_used, qualify_col,
						  &retrieved_attrs);
		appendStringInfoChar(buf, ')');

		/* Complete the CASE WHEN statement started above. */
		if (qualify_col)
			appendStringInfoString(buf, " END");

		table_close(rel, NoLock);
		bms_free(attrs_used);
	}
	else
	{
		char	   *colname = NULL;
		List	   *options;
		ListCell   *lc;

		/* varno must not be any of OUTER_VAR, INNER_VAR and INDEX_VAR. */
		Assert(!IS_SPECIAL_VARNO(varno));

		/*
		 * If it's a column of a foreign table, and it has the column_name FDW
		 * option, use that value.
		 */
		options = GetForeignColumnOptions(rte->relid, varattno);
		foreach(lc, options)
		{
			DefElem    *def = (DefElem *) lfirst(lc);

			if (strcmp(def->defname, "column_name") == 0)
			{
				colname = defGetString(def);
				break;
			}
		}

		/*
		 * If it's a column of a regular table or it doesn't have column_name
		 * FDW option, use attribute name.
		 */
		if (colname == NULL)
			colname = get_attname(rte->relid, varattno, false);

		if (qualify_col)
			ADD_REL_QUALIFIER(buf, varno);

		appendStringInfoString(buf, quote_identifier(colname));
	}
}

/*
 * Append remote name of specified foreign table to buf.
 * Use value of table_name FDW option (if any) instead of relation's name.
 * Similarly, schema_name FDW option overrides schema name.
 */
static void
deparseRelation(StringInfo buf, Relation rel)
{
	ForeignTable *table;
	const char *nspname = NULL;
	const char *relname = NULL;
	ListCell   *lc;

	/* obtain additional catalog information. */
	table = GetForeignTable(RelationGetRelid(rel));

	/*
	 * Use value of FDW options if any, instead of the name of object itself.
	 */
	foreach(lc, table->options)
	{
		DefElem    *def = (DefElem *) lfirst(lc);

		if (strcmp(def->defname, "schema_name") == 0)
			nspname = defGetString(def);
		else if (strcmp(def->defname, "table_name") == 0)
			relname = defGetString(def);
	}

	/*
	 * Note: we could skip printing the schema name if it's pg_catalog, but
	 * that doesn't seem worth the trouble.
	 */
	if (nspname == NULL)
		nspname = get_namespace_name(RelationGetNamespace(rel));
	if (relname == NULL)
		relname = RelationGetRelationName(rel);

	appendStringInfo(buf, "%s.%s",
					 quote_identifier(nspname), quote_identifier(relname));
}

/*
 * Append a SQL string literal representing "val" to buf.
 */
void
deparseStringLiteral(StringInfo buf, const char *val)
{
	const char *valptr;

	/*
	 * Rather than making assumptions about the remote server's value of
	 * standard_conforming_strings, always use E'foo' syntax if there are any
	 * backslashes.  This will fail on remote servers before 8.1, but those
	 * are long out of support.
	 */
	if (strchr(val, '\\') != NULL)
		appendStringInfoChar(buf, ESCAPE_STRING_SYNTAX);
	appendStringInfoChar(buf, '\'');
	for (valptr = val; *valptr; valptr++)
	{
		char		ch = *valptr;

		if (SQL_STR_DOUBLE(ch, true))
			appendStringInfoChar(buf, ch);
		appendStringInfoChar(buf, ch);
	}
	appendStringInfoChar(buf, '\'');
}

/*
 * Deparse given expression into context->buf.
 *
 * This function must support all the same node types that foreign_expr_walker
 * accepts.
 *
 * Note: unlike ruleutils.c, we just use a simple hard-wired parenthesization
 * scheme: anything more complex than a Var, Const, function call or cast
 * should be self-parenthesized.
 */
static void
deparseExpr(Expr *node, deparse_expr_cxt *context)
{
	if (node == NULL)
		return;

	switch (nodeTag(node))
	{
		case T_Var:
			deparseVar((Var *) node, context);
			break;
		case T_Const:
			deparseConst((Const *) node, context, 0);
			break;
		case T_Param:
			deparseParam((Param *) node, context);
			break;
		case T_SubscriptingRef:
			deparseSubscriptingRef((SubscriptingRef *) node, context);
			break;
		case T_FuncExpr:
			deparseFuncExpr((FuncExpr *) node, context);
			break;
		case T_OpExpr:
			deparseOpExpr((OpExpr *) node, context);
			break;
		case T_DistinctExpr:
			deparseDistinctExpr((DistinctExpr *) node, context);
			break;
		case T_ScalarArrayOpExpr:
			deparseScalarArrayOpExpr((ScalarArrayOpExpr *) node, context);
			break;
		case T_RelabelType:
			deparseRelabelType((RelabelType *) node, context);
			break;
		case T_BoolExpr:
			deparseBoolExpr((BoolExpr *) node, context);
			break;
		case T_NullTest:
			deparseNullTest((NullTest *) node, context);
			break;
		case T_CaseExpr:
			deparseCaseExpr((CaseExpr *) node, context);
			break;
		case T_ArrayExpr:
			deparseArrayExpr((ArrayExpr *) node, context);
			break;
		case T_Aggref:
			deparseAggref((Aggref *) node, context);
			break;
		default:
			elog(ERROR, "unsupported expression type for deparse: %d",
				 (int) nodeTag(node));
			break;
	}
}

/*
 * Deparse given Var node into context->buf.
 *
 * If the Var belongs to the foreign relation, just print its remote name.
 * Otherwise, it's effectively a Param (and will in fact be a Param at
 * run time).  Handle it the same way we handle plain Params --- see
 * deparseParam for comments.
 */
static void
deparseVar(Var *node, deparse_expr_cxt *context)
{
	Relids		relids = context->scanrel->relids;
	int			relno;
	int			colno;

	/* Qualify columns when multiple relations are involved. */
	bool		qualify_col = (bms_membership(relids) == BMS_MULTIPLE);

	/*
	 * If the Var belongs to the foreign relation that is deparsed as a
	 * subquery, use the relation and column alias to the Var provided by the
	 * subquery, instead of the remote name.
	 */
	if (is_subquery_var(node, context->scanrel, &relno, &colno))
	{
		appendStringInfo(context->buf, "%s%d.%s%d",
						 SUBQUERY_REL_ALIAS_PREFIX, relno,
						 SUBQUERY_COL_ALIAS_PREFIX, colno);
		return;
	}

	if (bms_is_member(node->varno, relids) && node->varlevelsup == 0)
		deparseColumnRef(context->buf, node->varno, node->varattno,
						 planner_rt_fetch(node->varno, context->root),
						 qualify_col);
	else
	{
		/* Treat like a Param */
		if (context->params_list)
		{
			int			pindex = 0;
			ListCell   *lc;

			/* find its index in params_list */
			foreach(lc, *context->params_list)
			{
				pindex++;
				if (equal(node, (Node *) lfirst(lc)))
					break;
			}
			if (lc == NULL)
			{
				/* not in list, so add it */
				pindex++;
				*context->params_list = lappend(*context->params_list, node);
			}

			printRemoteParam(pindex, node->vartype, node->vartypmod, context);
		}
		else
		{
			printRemotePlaceholder(node->vartype, node->vartypmod, context);
		}
	}
}

/*
 * Deparse given constant value into context->buf.
 *
 * This function has to be kept in sync with ruleutils.c's get_const_expr.
 *
 * As in that function, showtype can be -1 to never show "::typename"
 * decoration, +1 to always show it, or 0 to show it only if the constant
 * wouldn't be assumed to be the right type by default.
 *
 * In addition, this code allows showtype to be -2 to indicate that we should
 * not show "::typename" decoration if the constant is printed as an untyped
 * literal or NULL (while in other cases, behaving as for showtype == 0).
 */
static void
deparseConst(Const *node, deparse_expr_cxt *context, int showtype)
{
	StringInfo	buf = context->buf;
	Oid			typoutput;
	bool		typIsVarlena;
	char	   *extval;
	bool		isfloat = false;
	bool		isstring = false;
	bool		needlabel;

	if (node->constisnull)
	{
		appendStringInfoString(buf, "NULL");
		if (showtype >= 0)
			appendStringInfo(buf, "::%s",
							 deparse_type_name(node->consttype,
											   node->consttypmod));
		return;
	}

	getTypeOutputInfo(node->consttype,
					  &typoutput, &typIsVarlena);
	extval = OidOutputFunctionCall(typoutput, node->constvalue);

	switch (node->consttype)
	{
		case INT2OID:
		case INT4OID:
		case INT8OID:
		case OIDOID:
		case FLOAT4OID:
		case FLOAT8OID:
		case NUMERICOID:
			{
				/*
				 * No need to quote unless it's a special value such as 'NaN'.
				 * See comments in get_const_expr().
				 */
				if (strspn(extval, "0123456789+-eE.") == strlen(extval))
				{
					if (extval[0] == '+' || extval[0] == '-')
						appendStringInfo(buf, "(%s)", extval);
					else
						appendStringInfoString(buf, extval);
					if (strcspn(extval, "eE.") != strlen(extval))
						isfloat = true; /* it looks like a float */
				}
				else
					appendStringInfo(buf, "'%s'", extval);
			}
			break;
		case BITOID:
		case VARBITOID:
			appendStringInfo(buf, "B'%s'", extval);
			break;
		case BOOLOID:
			if (strcmp(extval, "t") == 0)
				appendStringInfoString(buf, "true");
			else
				appendStringInfoString(buf, "false");
			break;
		default:
			deparseStringLiteral(buf, extval);
			isstring = true;
			break;
	}

	pfree(extval);

	if (showtype == -1)
		return;					/* never print type label */

	/*
	 * For showtype == 0, append ::typename unless the constant will be
	 * implicitly typed as the right type when it is read in.
	 *
	 * XXX this code has to be kept in sync with the behavior of the parser,
	 * especially make_const.
	 */
	switch (node->consttype)
	{
		case BOOLOID:
		case INT4OID:
		case UNKNOWNOID:
			needlabel = false;
			break;
		case NUMERICOID:
			needlabel = !isfloat || (node->consttypmod >= 0);
			break;
		default:
			if (showtype == -2)
			{
				/* label unless we printed it as an untyped string */
				needlabel = !isstring;
			}
			else
				needlabel = true;
			break;
	}
	if (needlabel || showtype > 0)
		appendStringInfo(buf, "::%s",
						 deparse_type_name(node->consttype,
										   node->consttypmod));
}

/*
 * Deparse given Param node.
 *
 * If we're generating the query "for real", add the Param to
 * context->params_list if it's not already present, and then use its index
 * in that list as the remote parameter number.  During EXPLAIN, there's
 * no need to identify a parameter number.
 */
static void
deparseParam(Param *node, deparse_expr_cxt *context)
{
	if (context->params_list)
	{
		int			pindex = 0;
		ListCell   *lc;

		/* find its index in params_list */
		foreach(lc, *context->params_list)
		{
			pindex++;
			if (equal(node, (Node *) lfirst(lc)))
				break;
		}
		if (lc == NULL)
		{
			/* not in list, so add it */
			pindex++;
			*context->params_list = lappend(*context->params_list, node);
		}

		printRemoteParam(pindex, node->paramtype, node->paramtypmod, context);
	}
	else
	{
		printRemotePlaceholder(node->paramtype, node->paramtypmod, context);
	}
}

/*
 * Deparse a container subscript expression.
 */
static void
deparseSubscriptingRef(SubscriptingRef *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	ListCell   *lowlist_item;
	ListCell   *uplist_item;

	/* Always parenthesize the expression. */
	appendStringInfoChar(buf, '(');

	/*
	 * Deparse referenced array expression first.  If that expression includes
	 * a cast, we have to parenthesize to prevent the array subscript from
	 * being taken as typename decoration.  We can avoid that in the typical
	 * case of subscripting a Var, but otherwise do it.
	 */
	if (IsA(node->refexpr, Var))
		deparseExpr(node->refexpr, context);
	else
	{
		appendStringInfoChar(buf, '(');
		deparseExpr(node->refexpr, context);
		appendStringInfoChar(buf, ')');
	}

	/* Deparse subscript expressions. */
	lowlist_item = list_head(node->reflowerindexpr);	/* could be NULL */
	foreach(uplist_item, node->refupperindexpr)
	{
		appendStringInfoChar(buf, '[');
		if (lowlist_item)
		{
			deparseExpr(lfirst(lowlist_item), context);
			appendStringInfoChar(buf, ':');
			lowlist_item = lnext(node->reflowerindexpr, lowlist_item);
		}
		deparseExpr(lfirst(uplist_item), context);
		appendStringInfoChar(buf, ']');
	}

	appendStringInfoChar(buf, ')');
}

/*
 * Deparse a function call.
 */
static void
deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	bool		use_variadic;
	bool		first;
	ListCell   *arg;

	/*
	 * If the function call came from an implicit coercion, then just show the
	 * first argument.
	 */
	if (node->funcformat == COERCE_IMPLICIT_CAST)
	{
		deparseExpr((Expr *) linitial(node->args), context);
		return;
	}

	/*
	 * If the function call came from a cast, then show the first argument
	 * plus an explicit cast operation.
	 */
	if (node->funcformat == COERCE_EXPLICIT_CAST)
	{
		Oid			rettype = node->funcresulttype;
		int32		coercedTypmod;

		/* Get the typmod if this is a length-coercion function */
		(void) exprIsLengthCoercion((Node *) node, &coercedTypmod);

		deparseExpr((Expr *) linitial(node->args), context);
		appendStringInfo(buf, "::%s",
						 deparse_type_name(rettype, coercedTypmod));
		return;
	}

	/* Check if need to print VARIADIC (cf. ruleutils.c) */
	use_variadic = node->funcvariadic;

	/*
	 * Normal function: display as proname(args).
	 */
	appendFunctionName(node->funcid, context);
	appendStringInfoChar(buf, '(');

	/* ... and all the arguments */
	first = true;
	foreach(arg, node->args)
	{
		if (!first)
			appendStringInfoString(buf, ", ");
		if (use_variadic && lnext(node->args, arg) == NULL)
			appendStringInfoString(buf, "VARIADIC ");
		deparseExpr((Expr *) lfirst(arg), context);
		first = false;
	}
	appendStringInfoChar(buf, ')');
}

/*
 * Deparse given operator expression.   To avoid problems around
 * priority of operations, we always parenthesize the arguments.
 */
static void
deparseOpExpr(OpExpr *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	HeapTuple	tuple;
	Form_pg_operator form;
	Expr	   *right;
	bool		canSuppressRightConstCast = false;
	char		oprkind;

	/* Retrieve information about the operator from system catalog. */
	tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "cache lookup failed for operator %u", node->opno);
	form = (Form_pg_operator) GETSTRUCT(tuple);
	oprkind = form->oprkind;

	/* Sanity check. */
	Assert((oprkind == 'l' && list_length(node->args) == 1) ||
		   (oprkind == 'b' && list_length(node->args) == 2));

	right = llast(node->args);

	/* Always parenthesize the expression. */
	appendStringInfoChar(buf, '(');

	/* Deparse left operand, if any. */
	if (oprkind == 'b')
	{
		Expr	   *left = linitial(node->args);
		Oid			leftType = exprType((Node *) left);
		Oid			rightType = exprType((Node *) right);
		bool		canSuppressLeftConstCast = false;

		/*
		 * When considering a binary operator, if one operand is a Const that
		 * can be printed as a bare string literal or NULL (i.e., it will look
		 * like type UNKNOWN to the remote parser), the Const normally
		 * receives an explicit cast to the operator's input type.  However,
		 * in Const-to-Var comparisons where both operands are of the same
		 * type, we prefer to suppress the explicit cast, leaving the Const's
		 * type resolution up to the remote parser.  The remote's resolution
		 * heuristic will assume that an unknown input type being compared to
		 * a known input type is of that known type as well.
		 *
		 * This hack allows some cases to succeed where a remote column is
		 * declared with a different type in the local (foreign) table.  By
		 * emitting "foreigncol = 'foo'" not "foreigncol = 'foo'::text" or the
		 * like, we allow the remote parser to pick an "=" operator that's
		 * compatible with whatever type the remote column really is, such as
		 * an enum.
		 *
		 * We allow cast suppression to happen only when the other operand is
		 * a plain foreign Var.  Although the remote's unknown-type heuristic
		 * would apply to other cases just as well, we would be taking a
		 * bigger risk that the inferred type is something unexpected.  With
		 * this restriction, if anything goes wrong it's the user's fault for
		 * not declaring the local column with the same type as the remote
		 * column.
		 */
		if (leftType == rightType)
		{
			if (IsA(left, Const))
				canSuppressLeftConstCast = isPlainForeignVar(right, context);
			else if (IsA(right, Const))
				canSuppressRightConstCast = isPlainForeignVar(left, context);
		}

		if (canSuppressLeftConstCast)
			deparseConst((Const *) left, context, -2);
		else
			deparseExpr(left, context);

		appendStringInfoChar(buf, ' ');
	}

	/* Deparse operator name. */
	deparseOperatorName(buf, form);

	/* Deparse right operand. */
	appendStringInfoChar(buf, ' ');

	if (canSuppressRightConstCast)
		deparseConst((Const *) right, context, -2);
	else
		deparseExpr(right, context);

	appendStringInfoChar(buf, ')');

	ReleaseSysCache(tuple);
}

/*
 * Will "node" deparse as a plain foreign Var?
 */
static bool
isPlainForeignVar(Expr *node, deparse_expr_cxt *context)
{
	/*
	 * We allow the foreign Var to have an implicit RelabelType, mainly so
	 * that this'll work with varchar columns.  Note that deparseRelabelType
	 * will not print such a cast, so we're not breaking the restriction that
	 * the expression print as a plain Var.  We won't risk it for an implicit
	 * cast that requires a function, nor for non-implicit RelabelType; such
	 * cases seem too likely to involve semantics changes compared to what
	 * would happen on the remote side.
	 */
	if (IsA(node, RelabelType) &&
		((RelabelType *) node)->relabelformat == COERCE_IMPLICIT_CAST)
		node = ((RelabelType *) node)->arg;

	if (IsA(node, Var))
	{
		/*
		 * The Var must be one that'll deparse as a foreign column reference
		 * (cf. deparseVar).
		 */
		Var		   *var = (Var *) node;
		Relids		relids = context->scanrel->relids;

		if (bms_is_member(var->varno, relids) && var->varlevelsup == 0)
			return true;
	}

	return false;
}

/*
 * Print the name of an operator.
 */
static void
deparseOperatorName(StringInfo buf, Form_pg_operator opform)
{
	char	   *opname;

	/* opname is not a SQL identifier, so we should not quote it. */
	opname = NameStr(opform->oprname);

	/* Print schema name only if it's not pg_catalog */
	if (opform->oprnamespace != PG_CATALOG_NAMESPACE)
	{
		const char *opnspname;

		opnspname = get_namespace_name(opform->oprnamespace);
		/* Print fully qualified operator name. */
		appendStringInfo(buf, "OPERATOR(%s.%s)",
						 quote_identifier(opnspname), opname);
	}
	else
	{
		/* Just print operator name. */
		appendStringInfoString(buf, opname);
	}
}

/*
 * Deparse IS DISTINCT FROM.
 */
static void
deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;

	Assert(list_length(node->args) == 2);

	appendStringInfoChar(buf, '(');
	deparseExpr(linitial(node->args), context);
	appendStringInfoString(buf, " IS DISTINCT FROM ");
	deparseExpr(lsecond(node->args), context);
	appendStringInfoChar(buf, ')');
}

/*
 * Deparse given ScalarArrayOpExpr expression.  To avoid problems
 * around priority of operations, we always parenthesize the arguments.
 */
static void
deparseScalarArrayOpExpr(ScalarArrayOpExpr *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	HeapTuple	tuple;
	Form_pg_operator form;
	Expr	   *arg1;
	Expr	   *arg2;

	/* Retrieve information about the operator from system catalog. */
	tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "cache lookup failed for operator %u", node->opno);
	form = (Form_pg_operator) GETSTRUCT(tuple);

	/* Sanity check. */
	Assert(list_length(node->args) == 2);

	/* Always parenthesize the expression. */
	appendStringInfoChar(buf, '(');

	/* Deparse left operand. */
	arg1 = linitial(node->args);
	deparseExpr(arg1, context);
	appendStringInfoChar(buf, ' ');

	/* Deparse operator name plus decoration. */
	deparseOperatorName(buf, form);
	appendStringInfo(buf, " %s (", node->useOr ? "ANY" : "ALL");

	/* Deparse right operand. */
	arg2 = lsecond(node->args);
	deparseExpr(arg2, context);

	appendStringInfoChar(buf, ')');

	/* Always parenthesize the expression. */
	appendStringInfoChar(buf, ')');

	ReleaseSysCache(tuple);
}

/*
 * Deparse a RelabelType (binary-compatible cast) node.
 */
static void
deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
{
	deparseExpr(node->arg, context);
	if (node->relabelformat != COERCE_IMPLICIT_CAST)
		appendStringInfo(context->buf, "::%s",
						 deparse_type_name(node->resulttype,
										   node->resulttypmod));
}

/*
 * Deparse a BoolExpr node.
 */
static void
deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	const char *op = NULL;		/* keep compiler quiet */
	bool		first;
	ListCell   *lc;

	switch (node->boolop)
	{
		case AND_EXPR:
			op = "AND";
			break;
		case OR_EXPR:
			op = "OR";
			break;
		case NOT_EXPR:
			appendStringInfoString(buf, "(NOT ");
			deparseExpr(linitial(node->args), context);
			appendStringInfoChar(buf, ')');
			return;
	}

	appendStringInfoChar(buf, '(');
	first = true;
	foreach(lc, node->args)
	{
		if (!first)
			appendStringInfo(buf, " %s ", op);
		deparseExpr((Expr *) lfirst(lc), context);
		first = false;
	}
	appendStringInfoChar(buf, ')');
}

/*
 * Deparse IS [NOT] NULL expression.
 */
static void
deparseNullTest(NullTest *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;

	appendStringInfoChar(buf, '(');
	deparseExpr(node->arg, context);

	/*
	 * For scalar inputs, we prefer to print as IS [NOT] NULL, which is
	 * shorter and traditional.  If it's a rowtype input but we're applying a
	 * scalar test, must print IS [NOT] DISTINCT FROM NULL to be semantically
	 * correct.
	 */
	if (node->argisrow || !type_is_rowtype(exprType((Node *) node->arg)))
	{
		if (node->nulltesttype == IS_NULL)
			appendStringInfoString(buf, " IS NULL)");
		else
			appendStringInfoString(buf, " IS NOT NULL)");
	}
	else
	{
		if (node->nulltesttype == IS_NULL)
			appendStringInfoString(buf, " IS NOT DISTINCT FROM NULL)");
		else
			appendStringInfoString(buf, " IS DISTINCT FROM NULL)");
	}
}

/*
 * Deparse CASE expression
 */
static void
deparseCaseExpr(CaseExpr *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	ListCell   *lc;

	appendStringInfoString(buf, "(CASE");

	/* If this is a CASE arg WHEN then emit the arg expression */
	if (node->arg != NULL)
	{
		appendStringInfoChar(buf, ' ');
		deparseExpr(node->arg, context);
	}

	/* Add each condition/result of the CASE clause */
	foreach(lc, node->args)
	{
		CaseWhen   *whenclause = (CaseWhen *) lfirst(lc);

		/* WHEN */
		appendStringInfoString(buf, " WHEN ");
		if (node->arg == NULL)	/* CASE WHEN */
			deparseExpr(whenclause->expr, context);
		else					/* CASE arg WHEN */
		{
			/* Ignore the CaseTestExpr and equality operator. */
			deparseExpr(lsecond(castNode(OpExpr, whenclause->expr)->args),
						context);
		}

		/* THEN */
		appendStringInfoString(buf, " THEN ");
		deparseExpr(whenclause->result, context);
	}

	/* add ELSE if present */
	if (node->defresult != NULL)
	{
		appendStringInfoString(buf, " ELSE ");
		deparseExpr(node->defresult, context);
	}

	/* append END */
	appendStringInfoString(buf, " END)");
}

/*
 * Deparse ARRAY[...] construct.
 */
static void
deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	bool		first = true;
	ListCell   *lc;

	appendStringInfoString(buf, "ARRAY[");
	foreach(lc, node->elements)
	{
		if (!first)
			appendStringInfoString(buf, ", ");
		deparseExpr(lfirst(lc), context);
		first = false;
	}
	appendStringInfoChar(buf, ']');

	/* If the array is empty, we need an explicit cast to the array type. */
	if (node->elements == NIL)
		appendStringInfo(buf, "::%s",
						 deparse_type_name(node->array_typeid, -1));
}

/*
 * Deparse an Aggref node.
 */
static void
deparseAggref(Aggref *node, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	bool		use_variadic;

	/* Only basic, non-split aggregation accepted. */
	Assert(node->aggsplit == AGGSPLIT_SIMPLE);

	/* Check if need to print VARIADIC (cf. ruleutils.c) */
	use_variadic = node->aggvariadic;

	/* Find aggregate name from aggfnoid which is a pg_proc entry */
	appendFunctionName(node->aggfnoid, context);
	appendStringInfoChar(buf, '(');

	/* Add DISTINCT */
	appendStringInfoString(buf, (node->aggdistinct != NIL) ? "DISTINCT " : "");

	if (AGGKIND_IS_ORDERED_SET(node->aggkind))
	{
		/* Add WITHIN GROUP (ORDER BY ..) */
		ListCell   *arg;
		bool		first = true;

		Assert(!node->aggvariadic);
		Assert(node->aggorder != NIL);

		foreach(arg, node->aggdirectargs)
		{
			if (!first)
				appendStringInfoString(buf, ", ");
			first = false;

			deparseExpr((Expr *) lfirst(arg), context);
		}

		appendStringInfoString(buf, ") WITHIN GROUP (ORDER BY ");
		appendAggOrderBy(node->aggorder, node->args, context);
	}
	else
	{
		/* aggstar can be set only in zero-argument aggregates */
		if (node->aggstar)
			appendStringInfoChar(buf, '*');
		else
		{
			ListCell   *arg;
			bool		first = true;

			/* Add all the arguments */
			foreach(arg, node->args)
			{
				TargetEntry *tle = (TargetEntry *) lfirst(arg);
				Node	   *n = (Node *) tle->expr;

				if (tle->resjunk)
					continue;

				if (!first)
					appendStringInfoString(buf, ", ");
				first = false;

				/* Add VARIADIC */
				if (use_variadic && lnext(node->args, arg) == NULL)
					appendStringInfoString(buf, "VARIADIC ");

				deparseExpr((Expr *) n, context);
			}
		}

		/* Add ORDER BY */
		if (node->aggorder != NIL)
		{
			appendStringInfoString(buf, " ORDER BY ");
			appendAggOrderBy(node->aggorder, node->args, context);
		}
	}

	/* Add FILTER (WHERE ..) */
	if (node->aggfilter != NULL)
	{
		appendStringInfoString(buf, ") FILTER (WHERE ");
		deparseExpr((Expr *) node->aggfilter, context);
	}

	appendStringInfoChar(buf, ')');
}

/*
 * Append ORDER BY within aggregate function.
 */
static void
appendAggOrderBy(List *orderList, List *targetList, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	ListCell   *lc;
	bool		first = true;

	foreach(lc, orderList)
	{
		SortGroupClause *srt = (SortGroupClause *) lfirst(lc);
		Node	   *sortexpr;

		if (!first)
			appendStringInfoString(buf, ", ");
		first = false;

		/* Deparse the sort expression proper. */
		sortexpr = deparseSortGroupClause(srt->tleSortGroupRef, targetList,
										  false, context);
		/* Add decoration as needed. */
		appendOrderBySuffix(srt->sortop, exprType(sortexpr), srt->nulls_first,
							context);
	}
}

/*
 * Append the ASC, DESC, USING <OPERATOR> and NULLS FIRST / NULLS LAST parts
 * of an ORDER BY clause.
 */
static void
appendOrderBySuffix(Oid sortop, Oid sortcoltype, bool nulls_first,
					deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	TypeCacheEntry *typentry;

	/* See whether operator is default < or > for sort expr's datatype. */
	typentry = lookup_type_cache(sortcoltype,
								 TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);

	if (sortop == typentry->lt_opr)
		appendStringInfoString(buf, " ASC");
	else if (sortop == typentry->gt_opr)
		appendStringInfoString(buf, " DESC");
	else
	{
		HeapTuple	opertup;
		Form_pg_operator operform;

		appendStringInfoString(buf, " USING ");

		/* Append operator name. */
		opertup = SearchSysCache1(OPEROID, ObjectIdGetDatum(sortop));
		if (!HeapTupleIsValid(opertup))
			elog(ERROR, "cache lookup failed for operator %u", sortop);
		operform = (Form_pg_operator) GETSTRUCT(opertup);
		deparseOperatorName(buf, operform);
		ReleaseSysCache(opertup);
	}

	if (nulls_first)
		appendStringInfoString(buf, " NULLS FIRST");
	else
		appendStringInfoString(buf, " NULLS LAST");
}

/*
 * Print the representation of a parameter to be sent to the remote side.
 *
 * Note: we always label the Param's type explicitly rather than relying on
 * transmitting a numeric type OID in PQexecParams().  This allows us to
 * avoid assuming that types have the same OIDs on the remote side as they
 * do locally --- they need only have the same names.
 */
static void
printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
				 deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	char	   *ptypename = deparse_type_name(paramtype, paramtypmod);

	appendStringInfo(buf, "$%d::%s", paramindex, ptypename);
}

/*
 * Print the representation of a placeholder for a parameter that will be
 * sent to the remote side at execution time.
 *
 * This is used when we're just trying to EXPLAIN the remote query.
 * We don't have the actual value of the runtime parameter yet, and we don't
 * want the remote planner to generate a plan that depends on such a value
 * anyway.  Thus, we can't do something simple like "$1::paramtype".
 * Instead, we emit "((SELECT null::paramtype)::paramtype)".
 * In all extant versions of Postgres, the planner will see that as an unknown
 * constant value, which is what we want.  This might need adjustment if we
 * ever make the planner flatten scalar subqueries.  Note: the reason for the
 * apparently useless outer cast is to ensure that the representation as a
 * whole will be parsed as an a_expr and not a select_with_parens; the latter
 * would do the wrong thing in the context "x = ANY(...)".
 */
static void
printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
					   deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	char	   *ptypename = deparse_type_name(paramtype, paramtypmod);

	appendStringInfo(buf, "((SELECT null::%s)::%s)", ptypename, ptypename);
}

/*
 * Deparse GROUP BY clause.
 */
static void
appendGroupByClause(List *tlist, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	Query	   *query = context->root->parse;
	ListCell   *lc;
	bool		first = true;

	/* Nothing to be done, if there's no GROUP BY clause in the query. */
	if (!query->groupClause)
		return;

	appendStringInfoString(buf, " GROUP BY ");

	/*
	 * Queries with grouping sets are not pushed down, so we don't expect
	 * grouping sets here.
	 */
	Assert(!query->groupingSets);

	/*
	 * We intentionally print query->groupClause not processed_groupClause,
	 * leaving it to the remote planner to get rid of any redundant GROUP BY
	 * items again.  This is necessary in case processed_groupClause reduced
	 * to empty, and in any case the redundancy situation on the remote might
	 * be different than what we think here.
	 */
	foreach(lc, query->groupClause)
	{
		SortGroupClause *grp = (SortGroupClause *) lfirst(lc);

		if (!first)
			appendStringInfoString(buf, ", ");
		first = false;

		deparseSortGroupClause(grp->tleSortGroupRef, tlist, true, context);
	}
}

/*
 * Deparse ORDER BY clause defined by the given pathkeys.
 *
 * The clause should use Vars from context->scanrel if !has_final_sort,
 * or from context->foreignrel's targetlist if has_final_sort.
 *
 * We find a suitable pathkey expression (some earlier step
 * should have verified that there is one) and deparse it.
 */
static void
appendOrderByClause(List *pathkeys, bool has_final_sort,
					deparse_expr_cxt *context)
{
	ListCell   *lcell;
	int			nestlevel;
	StringInfo	buf = context->buf;
	bool		gotone = false;

	/* Make sure any constants in the exprs are printed portably */
	nestlevel = set_transmission_modes();

	foreach(lcell, pathkeys)
	{
		PathKey    *pathkey = lfirst(lcell);
		EquivalenceMember *em;
		Expr	   *em_expr;
		Oid			oprid;

		if (has_final_sort)
		{
			/*
			 * By construction, context->foreignrel is the input relation to
			 * the final sort.
			 */
			em = find_em_for_rel_target(context->root,
										pathkey->pk_eclass,
										context->foreignrel);
		}
		else
			em = find_em_for_rel(context->root,
								 pathkey->pk_eclass,
								 context->scanrel);

		/*
		 * We don't expect any error here; it would mean that shippability
		 * wasn't verified earlier.  For the same reason, we don't recheck
		 * shippability of the sort operator.
		 */
		if (em == NULL)
			elog(ERROR, "could not find pathkey item to sort");

		em_expr = em->em_expr;

		/*
		 * If the member is a Const expression then we needn't add it to the
		 * ORDER BY clause.  This can happen in UNION ALL queries where the
		 * union child targetlist has a Const.  Adding these would be
		 * wasteful, but also, for INT columns, an integer literal would be
		 * seen as an ordinal column position rather than a value to sort by.
		 * deparseConst() does have code to handle this, but it seems less
		 * effort on all accounts just to skip these for ORDER BY clauses.
		 */
		if (IsA(em_expr, Const))
			continue;

		if (!gotone)
		{
			appendStringInfoString(buf, " ORDER BY ");
			gotone = true;
		}
		else
			appendStringInfoString(buf, ", ");

		/*
		 * Lookup the operator corresponding to the strategy in the opclass.
		 * The datatype used by the opfamily is not necessarily the same as
		 * the expression type (for array types for example).
		 */
		oprid = get_opfamily_member(pathkey->pk_opfamily,
									em->em_datatype,
									em->em_datatype,
									pathkey->pk_strategy);
		if (!OidIsValid(oprid))
			elog(ERROR, "missing operator %d(%u,%u) in opfamily %u",
				 pathkey->pk_strategy, em->em_datatype, em->em_datatype,
				 pathkey->pk_opfamily);

		deparseExpr(em_expr, context);

		/*
		 * Here we need to use the expression's actual type to discover
		 * whether the desired operator will be the default or not.
		 */
		appendOrderBySuffix(oprid, exprType((Node *) em_expr),
							pathkey->pk_nulls_first, context);

	}
	reset_transmission_modes(nestlevel);
}

/*
 * Deparse LIMIT/OFFSET clause.
 */
static void
appendLimitClause(deparse_expr_cxt *context)
{
	PlannerInfo *root = context->root;
	StringInfo	buf = context->buf;
	int			nestlevel;

	/* Make sure any constants in the exprs are printed portably */
	nestlevel = set_transmission_modes();

	if (root->parse->limitCount)
	{
		appendStringInfoString(buf, " LIMIT ");
		deparseExpr((Expr *) root->parse->limitCount, context);
	}
	if (root->parse->limitOffset)
	{
		appendStringInfoString(buf, " OFFSET ");
		deparseExpr((Expr *) root->parse->limitOffset, context);
	}

	reset_transmission_modes(nestlevel);
}

/*
 * appendFunctionName
 *		Deparses function name from given function oid.
 */
static void
appendFunctionName(Oid funcid, deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	HeapTuple	proctup;
	Form_pg_proc procform;
	const char *proname;

	proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
	if (!HeapTupleIsValid(proctup))
		elog(ERROR, "cache lookup failed for function %u", funcid);
	procform = (Form_pg_proc) GETSTRUCT(proctup);

	/* Print schema name only if it's not pg_catalog */
	if (procform->pronamespace != PG_CATALOG_NAMESPACE)
	{
		const char *schemaname;

		schemaname = get_namespace_name(procform->pronamespace);
		appendStringInfo(buf, "%s.", quote_identifier(schemaname));
	}

	/* Always print the function name */
	proname = NameStr(procform->proname);
	appendStringInfoString(buf, quote_identifier(proname));

	ReleaseSysCache(proctup);
}

/*
 * Appends a sort or group clause.
 *
 * Like get_rule_sortgroupclause(), returns the expression tree, so caller
 * need not find it again.
 */
static Node *
deparseSortGroupClause(Index ref, List *tlist, bool force_colno,
					   deparse_expr_cxt *context)
{
	StringInfo	buf = context->buf;
	TargetEntry *tle;
	Expr	   *expr;

	tle = get_sortgroupref_tle(ref, tlist);
	expr = tle->expr;

	if (force_colno)
	{
		/* Use column-number form when requested by caller. */
		Assert(!tle->resjunk);
		appendStringInfo(buf, "%d", tle->resno);
	}
	else if (expr && IsA(expr, Const))
	{
		/*
		 * Force a typecast here so that we don't emit something like "GROUP
		 * BY 2", which will be misconstrued as a column position rather than
		 * a constant.
		 */
		deparseConst((Const *) expr, context, 1);
	}
	else if (!expr || IsA(expr, Var))
		deparseExpr(expr, context);
	else
	{
		/* Always parenthesize the expression. */
		appendStringInfoChar(buf, '(');
		deparseExpr(expr, context);
		appendStringInfoChar(buf, ')');
	}

	return (Node *) expr;
}


/*
 * Returns true if given Var is deparsed as a subquery output column, in
 * which case, *relno and *colno are set to the IDs for the relation and
 * column alias to the Var provided by the subquery.
 */
static bool
is_subquery_var(Var *node, RelOptInfo *foreignrel, int *relno, int *colno)
{
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
	RelOptInfo *outerrel = fpinfo->outerrel;
	RelOptInfo *innerrel = fpinfo->innerrel;

	/* Should only be called in these cases. */
	Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

	/*
	 * If the given relation isn't a join relation, it doesn't have any lower
	 * subqueries, so the Var isn't a subquery output column.
	 */
	if (!IS_JOIN_REL(foreignrel))
		return false;

	/*
	 * If the Var doesn't belong to any lower subqueries, it isn't a subquery
	 * output column.
	 */
	if (!bms_is_member(node->varno, fpinfo->lower_subquery_rels))
		return false;

	if (bms_is_member(node->varno, outerrel->relids))
	{
		/*
		 * If outer relation is deparsed as a subquery, the Var is an output
		 * column of the subquery; get the IDs for the relation/column alias.
		 */
		if (fpinfo->make_outerrel_subquery)
		{
			get_relation_column_alias_ids(node, outerrel, relno, colno);
			return true;
		}

		/* Otherwise, recurse into the outer relation. */
		return is_subquery_var(node, outerrel, relno, colno);
	}
	else
	{
		Assert(bms_is_member(node->varno, innerrel->relids));

		/*
		 * If inner relation is deparsed as a subquery, the Var is an output
		 * column of the subquery; get the IDs for the relation/column alias.
		 */
		if (fpinfo->make_innerrel_subquery)
		{
			get_relation_column_alias_ids(node, innerrel, relno, colno);
			return true;
		}

		/* Otherwise, recurse into the inner relation. */
		return is_subquery_var(node, innerrel, relno, colno);
	}
}

/*
 * Get the IDs for the relation and column alias to given Var belonging to
 * given relation, which are returned into *relno and *colno.
 */
static void
get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
							  int *relno, int *colno)
{
	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
	int			i;
	ListCell   *lc;

	/* Get the relation alias ID */
	*relno = fpinfo->relation_index;

	/* Get the column alias ID */
	i = 1;
	foreach(lc, foreignrel->reltarget->exprs)
	{
		Var		   *tlvar = (Var *) lfirst(lc);

		/*
		 * Match reltarget entries only on varno/varattno.  Ideally there
		 * would be some cross-check on varnullingrels, but it's unclear what
		 * to do exactly; we don't have enough context to know what that value
		 * should be.
		 */
		if (IsA(tlvar, Var) &&
			tlvar->varno == node->varno &&
			tlvar->varattno == node->varattno)
		{
			*colno = i;
			return;
		}
		i++;
	}

	/* Shouldn't get here */
	elog(ERROR, "unexpected expression in subquery output");
}