Adding upstream version 13.4.upstream/13.4upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3446 insertions, 0 deletions

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
new file mode 100644
index 0000000..2029036
--- /dev/null
+++ b/contrib/postgres_fdw/deparse.c
@@ -0,0 +1,3446 @@
+/*-------------------------------------------------------------------------
+ *
+ * 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) 2012-2020, 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_collation.h"
+#include "catalog/pg_namespace.h"
+#include "catalog/pg_operator.h"
+#include "catalog/pg_proc.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"
+
+/*
+ * 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);
+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 *expr, 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 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 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 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))
+		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.
+ *
+ * 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)
+{
+	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;
+
+				/*
+				 * 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 to remaining subexpressions.  Since the container
+				 * subscripts must yield (noncollatable) integers, they won't
+				 * affect the inner_cxt state.
+				 */
+				if (!foreign_expr_walker((Node *) sr->refupperindexpr,
+										 glob_cxt, &inner_cxt))
+					return false;
+				if (!foreign_expr_walker((Node *) sr->reflowerindexpr,
+										 glob_cxt, &inner_cxt))
+					return false;
+				if (!foreign_expr_walker((Node *) sr->refexpr,
+										 glob_cxt, &inner_cxt))
+					return false;
+
+				/*
+				 * Container subscripting should yield same collation as
+				 * input, but for safety 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))
+					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))
+					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))
+					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))
+					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))
+					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))
+					return false;
+
+				/* Output is always boolean and so noncollatable. */
+				collation = InvalidOid;
+				state = FDW_COLLATE_NONE;
+			}
+			break;
+		case T_ArrayExpr:
+			{
+				ArrayExpr  *a = (ArrayExpr *) node;
+
+				/*
+				 * Recurse to input subexpressions.
+				 */
+				if (!foreign_expr_walker((Node *) a->elements,
+										 glob_cxt, &inner_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))
+						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))
+						return false;
+				}
+
+				/*
+				 * For aggorder elements, check whether the sort operator, if
+				 * specified, is shippable or not.
+				 */
+				if (agg->aggorder)
+				{
+					ListCell   *lc;
+
+					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))
+					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;
+}
+
+/*
+ * 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 (relid == root->parse->resultRelation &&
+			(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.
+ */
+void
+deparseInsertSql(StringInfo buf, RangeTblEntry *rte,
+				 Index rtindex, Relation rel,
+				 List *targetAttrs, bool doNothing,
+				 List *withCheckOptionList, List *returningList,
+				 List **retrieved_attrs)
+{
+	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");
+
+	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);
+}
+
+/*
+ * 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
+ * '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;
+	ListCell   *lc;
+	RangeTblEntry *rte = planner_rt_fetch(rtindex, root);
+
+	/* 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;
+	foreach(lc, targetAttrs)
+	{
+		int			attnum = lfirst_int(lc);
+		TargetEntry *tle = get_tle_by_resno(targetlist, attnum);
+
+		if (!tle)
+			elog(ERROR, "attribute number %d not found in UPDATE targetlist",
+				 attnum);
+
+		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 sample rows of given relation.
+ *
+ * SELECT command is appended to buf, and list of columns retrieved
+ * is returned to *retrieved_attrs.
+ */
+void
+deparseAnalyzeSql(StringInfo buf, Relation rel, 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
+	 */
+	appendStringInfoString(buf, " FROM ");
+	deparseRelation(buf, rel);
+}
+
+/*
+ * 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_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 for that function, showtype can be -1 to never show "::typename" decoration,
+ * or +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.
+ */
+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		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);
+			break;
+	}
+
+	pfree(extval);
+
+	if (showtype < 0)
+		return;
+
+	/*
+	 * 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:
+			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;
+	char		oprkind;
+	ListCell   *arg;
+
+	/* 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 == 'r' && list_length(node->args) == 1) ||
+		   (oprkind == 'l' && list_length(node->args) == 1) ||
+		   (oprkind == 'b' && list_length(node->args) == 2));
+
+	/* Always parenthesize the expression. */
+	appendStringInfoChar(buf, '(');
+
+	/* Deparse left operand. */
+	if (oprkind == 'r' || oprkind == 'b')
+	{
+		arg = list_head(node->args);
+		deparseExpr(lfirst(arg), context);
+		appendStringInfoChar(buf, ' ');
+	}
+
+	/* Deparse operator name. */
+	deparseOperatorName(buf, form);
+
+	/* Deparse right operand. */
+	if (oprkind == 'l' || oprkind == 'b')
+	{
+		arg = list_tail(node->args);
+		appendStringInfoChar(buf, ' ');
+		deparseExpr(lfirst(arg), context);
+	}
+
+	appendStringInfoChar(buf, ')');
+
+	ReleaseSysCache(tuple);
+}
+
+/*
+ * 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 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;
+		Oid			sortcoltype;
+		TypeCacheEntry *typentry;
+
+		if (!first)
+			appendStringInfoString(buf, ", ");
+		first = false;
+
+		sortexpr = deparseSortGroupClause(srt->tleSortGroupRef, targetList,
+										  false, context);
+		sortcoltype = exprType(sortexpr);
+		/* See whether operator is default < or > for datatype */
+		typentry = lookup_type_cache(sortcoltype,
+									 TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
+		if (srt->sortop == typentry->lt_opr)
+			appendStringInfoString(buf, " ASC");
+		else if (srt->sortop == typentry->gt_opr)
+			appendStringInfoString(buf, " DESC");
+		else
+		{
+			HeapTuple	opertup;
+			Form_pg_operator operform;
+
+			appendStringInfoString(buf, " USING ");
+
+			/* Append operator name. */
+			opertup = SearchSysCache1(OPEROID, ObjectIdGetDatum(srt->sortop));
+			if (!HeapTupleIsValid(opertup))
+				elog(ERROR, "cache lookup failed for operator %u", srt->sortop);
+			operform = (Form_pg_operator) GETSTRUCT(opertup);
+			deparseOperatorName(buf, operform);
+			ReleaseSysCache(opertup);
+		}
+
+		if (srt->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);
+
+	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 according to the given pathkeys for given base
+ * relation. From given pathkeys expressions belonging entirely to the given
+ * base relation are obtained and deparsed.
+ */
+static void
+appendOrderByClause(List *pathkeys, bool has_final_sort,
+					deparse_expr_cxt *context)
+{
+	ListCell   *lcell;
+	int			nestlevel;
+	char	   *delim = " ";
+	RelOptInfo *baserel = context->scanrel;
+	StringInfo	buf = context->buf;
+
+	/* Make sure any constants in the exprs are printed portably */
+	nestlevel = set_transmission_modes();
+
+	appendStringInfoString(buf, " ORDER BY");
+	foreach(lcell, pathkeys)
+	{
+		PathKey    *pathkey = lfirst(lcell);
+		Expr	   *em_expr;
+
+		if (has_final_sort)
+		{
+			/*
+			 * By construction, context->foreignrel is the input relation to
+			 * the final sort.
+			 */
+			em_expr = find_em_expr_for_input_target(context->root,
+													pathkey->pk_eclass,
+													context->foreignrel->reltarget);
+		}
+		else
+			em_expr = find_em_expr_for_rel(pathkey->pk_eclass, baserel);
+
+		Assert(em_expr != NULL);
+
+		appendStringInfoString(buf, delim);
+		deparseExpr(em_expr, context);
+		if (pathkey->pk_strategy == BTLessStrategyNumber)
+			appendStringInfoString(buf, " ASC");
+		else
+			appendStringInfoString(buf, " DESC");
+
+		if (pathkey->pk_nulls_first)
+			appendStringInfoString(buf, " NULLS FIRST");
+		else
+			appendStringInfoString(buf, " NULLS LAST");
+
+		delim = ", ";
+	}
+	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)
+	{
+		if (equal(lfirst(lc), (Node *) node))
+		{
+			*colno = i;
+			return;
+		}
+		i++;
+	}
+
+	/* Shouldn't get here */
+	elog(ERROR, "unexpected expression in subquery output");
+}