Adding upstream version 14.5.upstream/14.5upstream

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

1 files changed, 1120 insertions, 0 deletions

diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
new file mode 100644
index 0000000..37eb64b
--- /dev/null
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -0,0 +1,1120 @@
+/*-------------------------------------------------------------------------
+ *
+ * analyzejoins.c
+ *	  Routines for simplifying joins after initial query analysis
+ *
+ * While we do a great deal of join simplification in prep/prepjointree.c,
+ * certain optimizations cannot be performed at that stage for lack of
+ * detailed information about the query.  The routines here are invoked
+ * after initsplan.c has done its work, and can do additional join removal
+ * and simplification steps based on the information extracted.  The penalty
+ * is that we have to work harder to clean up after ourselves when we modify
+ * the query, since the derived data structures have to be updated too.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/optimizer/plan/analyzejoins.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "nodes/nodeFuncs.h"
+#include "optimizer/clauses.h"
+#include "optimizer/joininfo.h"
+#include "optimizer/optimizer.h"
+#include "optimizer/pathnode.h"
+#include "optimizer/paths.h"
+#include "optimizer/planmain.h"
+#include "optimizer/tlist.h"
+#include "utils/lsyscache.h"
+
+/* local functions */
+static bool join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo);
+static void remove_rel_from_query(PlannerInfo *root, int relid,
+								  Relids joinrelids);
+static List *remove_rel_from_joinlist(List *joinlist, int relid, int *nremoved);
+static bool rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel);
+static bool rel_is_distinct_for(PlannerInfo *root, RelOptInfo *rel,
+								List *clause_list);
+static Oid	distinct_col_search(int colno, List *colnos, List *opids);
+static bool is_innerrel_unique_for(PlannerInfo *root,
+								   Relids joinrelids,
+								   Relids outerrelids,
+								   RelOptInfo *innerrel,
+								   JoinType jointype,
+								   List *restrictlist);
+
+
+/*
+ * remove_useless_joins
+ *		Check for relations that don't actually need to be joined at all,
+ *		and remove them from the query.
+ *
+ * We are passed the current joinlist and return the updated list.  Other
+ * data structures that have to be updated are accessible via "root".
+ */
+List *
+remove_useless_joins(PlannerInfo *root, List *joinlist)
+{
+	ListCell   *lc;
+
+	/*
+	 * We are only interested in relations that are left-joined to, so we can
+	 * scan the join_info_list to find them easily.
+	 */
+restart:
+	foreach(lc, root->join_info_list)
+	{
+		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
+		int			innerrelid;
+		int			nremoved;
+
+		/* Skip if not removable */
+		if (!join_is_removable(root, sjinfo))
+			continue;
+
+		/*
+		 * Currently, join_is_removable can only succeed when the sjinfo's
+		 * righthand is a single baserel.  Remove that rel from the query and
+		 * joinlist.
+		 */
+		innerrelid = bms_singleton_member(sjinfo->min_righthand);
+
+		remove_rel_from_query(root, innerrelid,
+							  bms_union(sjinfo->min_lefthand,
+										sjinfo->min_righthand));
+
+		/* We verify that exactly one reference gets removed from joinlist */
+		nremoved = 0;
+		joinlist = remove_rel_from_joinlist(joinlist, innerrelid, &nremoved);
+		if (nremoved != 1)
+			elog(ERROR, "failed to find relation %d in joinlist", innerrelid);
+
+		/*
+		 * We can delete this SpecialJoinInfo from the list too, since it's no
+		 * longer of interest.  (Since we'll restart the foreach loop
+		 * immediately, we don't bother with foreach_delete_current.)
+		 */
+		root->join_info_list = list_delete_cell(root->join_info_list, lc);
+
+		/*
+		 * Restart the scan.  This is necessary to ensure we find all
+		 * removable joins independently of ordering of the join_info_list
+		 * (note that removal of attr_needed bits may make a join appear
+		 * removable that did not before).
+		 */
+		goto restart;
+	}
+
+	return joinlist;
+}
+
+/*
+ * clause_sides_match_join
+ *	  Determine whether a join clause is of the right form to use in this join.
+ *
+ * We already know that the clause is a binary opclause referencing only the
+ * rels in the current join.  The point here is to check whether it has the
+ * form "outerrel_expr op innerrel_expr" or "innerrel_expr op outerrel_expr",
+ * rather than mixing outer and inner vars on either side.  If it matches,
+ * we set the transient flag outer_is_left to identify which side is which.
+ */
+static inline bool
+clause_sides_match_join(RestrictInfo *rinfo, Relids outerrelids,
+						Relids innerrelids)
+{
+	if (bms_is_subset(rinfo->left_relids, outerrelids) &&
+		bms_is_subset(rinfo->right_relids, innerrelids))
+	{
+		/* lefthand side is outer */
+		rinfo->outer_is_left = true;
+		return true;
+	}
+	else if (bms_is_subset(rinfo->left_relids, innerrelids) &&
+			 bms_is_subset(rinfo->right_relids, outerrelids))
+	{
+		/* righthand side is outer */
+		rinfo->outer_is_left = false;
+		return true;
+	}
+	return false;				/* no good for these input relations */
+}
+
+/*
+ * join_is_removable
+ *	  Check whether we need not perform this special join at all, because
+ *	  it will just duplicate its left input.
+ *
+ * This is true for a left join for which the join condition cannot match
+ * more than one inner-side row.  (There are other possibly interesting
+ * cases, but we don't have the infrastructure to prove them.)  We also
+ * have to check that the inner side doesn't generate any variables needed
+ * above the join.
+ */
+static bool
+join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
+{
+	int			innerrelid;
+	RelOptInfo *innerrel;
+	Relids		joinrelids;
+	List	   *clause_list = NIL;
+	ListCell   *l;
+	int			attroff;
+
+	/*
+	 * Must be a non-delaying left join to a single baserel, else we aren't
+	 * going to be able to do anything with it.
+	 */
+	if (sjinfo->jointype != JOIN_LEFT ||
+		sjinfo->delay_upper_joins)
+		return false;
+
+	if (!bms_get_singleton_member(sjinfo->min_righthand, &innerrelid))
+		return false;
+
+	innerrel = find_base_rel(root, innerrelid);
+
+	/*
+	 * Before we go to the effort of checking whether any innerrel variables
+	 * are needed above the join, make a quick check to eliminate cases in
+	 * which we will surely be unable to prove uniqueness of the innerrel.
+	 */
+	if (!rel_supports_distinctness(root, innerrel))
+		return false;
+
+	/* Compute the relid set for the join we are considering */
+	joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
+
+	/*
+	 * We can't remove the join if any inner-rel attributes are used above the
+	 * join.
+	 *
+	 * Note that this test only detects use of inner-rel attributes in higher
+	 * join conditions and the target list.  There might be such attributes in
+	 * pushed-down conditions at this join, too.  We check that case below.
+	 *
+	 * As a micro-optimization, it seems better to start with max_attr and
+	 * count down rather than starting with min_attr and counting up, on the
+	 * theory that the system attributes are somewhat less likely to be wanted
+	 * and should be tested last.
+	 */
+	for (attroff = innerrel->max_attr - innerrel->min_attr;
+		 attroff >= 0;
+		 attroff--)
+	{
+		if (!bms_is_subset(innerrel->attr_needed[attroff], joinrelids))
+			return false;
+	}
+
+	/*
+	 * Similarly check that the inner rel isn't needed by any PlaceHolderVars
+	 * that will be used above the join.  We only need to fail if such a PHV
+	 * actually references some inner-rel attributes; but the correct check
+	 * for that is relatively expensive, so we first check against ph_eval_at,
+	 * which must mention the inner rel if the PHV uses any inner-rel attrs as
+	 * non-lateral references.  Note that if the PHV's syntactic scope is just
+	 * the inner rel, we can't drop the rel even if the PHV is variable-free.
+	 */
+	foreach(l, root->placeholder_list)
+	{
+		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
+
+		if (bms_overlap(phinfo->ph_lateral, innerrel->relids))
+			return false;		/* it references innerrel laterally */
+		if (bms_is_subset(phinfo->ph_needed, joinrelids))
+			continue;			/* PHV is not used above the join */
+		if (!bms_overlap(phinfo->ph_eval_at, innerrel->relids))
+			continue;			/* it definitely doesn't reference innerrel */
+		if (bms_is_subset(phinfo->ph_eval_at, innerrel->relids))
+			return false;		/* there isn't any other place to eval PHV */
+		if (bms_overlap(pull_varnos(root, (Node *) phinfo->ph_var->phexpr),
+						innerrel->relids))
+			return false;		/* it does reference innerrel */
+	}
+
+	/*
+	 * Search for mergejoinable clauses that constrain the inner rel against
+	 * either the outer rel or a pseudoconstant.  If an operator is
+	 * mergejoinable then it behaves like equality for some btree opclass, so
+	 * it's what we want.  The mergejoinability test also eliminates clauses
+	 * containing volatile functions, which we couldn't depend on.
+	 */
+	foreach(l, innerrel->joininfo)
+	{
+		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);
+
+		/*
+		 * If it's not a join clause for this outer join, we can't use it.
+		 * Note that if the clause is pushed-down, then it is logically from
+		 * above the outer join, even if it references no other rels (it might
+		 * be from WHERE, for example).
+		 */
+		if (RINFO_IS_PUSHED_DOWN(restrictinfo, joinrelids))
+		{
+			/*
+			 * If such a clause actually references the inner rel then join
+			 * removal has to be disallowed.  We have to check this despite
+			 * the previous attr_needed checks because of the possibility of
+			 * pushed-down clauses referencing the rel.
+			 */
+			if (bms_is_member(innerrelid, restrictinfo->clause_relids))
+				return false;
+			continue;			/* else, ignore; not useful here */
+		}
+
+		/* Ignore if it's not a mergejoinable clause */
+		if (!restrictinfo->can_join ||
+			restrictinfo->mergeopfamilies == NIL)
+			continue;			/* not mergejoinable */
+
+		/*
+		 * Check if clause has the form "outer op inner" or "inner op outer",
+		 * and if so mark which side is inner.
+		 */
+		if (!clause_sides_match_join(restrictinfo, sjinfo->min_lefthand,
+									 innerrel->relids))
+			continue;			/* no good for these input relations */
+
+		/* OK, add to list */
+		clause_list = lappend(clause_list, restrictinfo);
+	}
+
+	/*
+	 * Now that we have the relevant equality join clauses, try to prove the
+	 * innerrel distinct.
+	 */
+	if (rel_is_distinct_for(root, innerrel, clause_list))
+		return true;
+
+	/*
+	 * Some day it would be nice to check for other methods of establishing
+	 * distinctness.
+	 */
+	return false;
+}
+
+
+/*
+ * Remove the target relid from the planner's data structures, having
+ * determined that there is no need to include it in the query.
+ *
+ * We are not terribly thorough here.  We must make sure that the rel is
+ * no longer treated as a baserel, and that attributes of other baserels
+ * are no longer marked as being needed at joins involving this rel.
+ * Also, join quals involving the rel have to be removed from the joininfo
+ * lists, but only if they belong to the outer join identified by joinrelids.
+ */
+static void
+remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
+{
+	RelOptInfo *rel = find_base_rel(root, relid);
+	List	   *joininfos;
+	Index		rti;
+	ListCell   *l;
+
+	/*
+	 * Mark the rel as "dead" to show it is no longer part of the join tree.
+	 * (Removing it from the baserel array altogether seems too risky.)
+	 */
+	rel->reloptkind = RELOPT_DEADREL;
+
+	/*
+	 * Remove references to the rel from other baserels' attr_needed arrays.
+	 */
+	for (rti = 1; rti < root->simple_rel_array_size; rti++)
+	{
+		RelOptInfo *otherrel = root->simple_rel_array[rti];
+		int			attroff;
+
+		/* there may be empty slots corresponding to non-baserel RTEs */
+		if (otherrel == NULL)
+			continue;
+
+		Assert(otherrel->relid == rti); /* sanity check on array */
+
+		/* no point in processing target rel itself */
+		if (otherrel == rel)
+			continue;
+
+		for (attroff = otherrel->max_attr - otherrel->min_attr;
+			 attroff >= 0;
+			 attroff--)
+		{
+			otherrel->attr_needed[attroff] =
+				bms_del_member(otherrel->attr_needed[attroff], relid);
+		}
+	}
+
+	/*
+	 * Likewise remove references from SpecialJoinInfo data structures.
+	 *
+	 * This is relevant in case the outer join we're deleting is nested inside
+	 * other outer joins: the upper joins' relid sets have to be adjusted. The
+	 * RHS of the target outer join will be made empty here, but that's OK
+	 * since caller will delete that SpecialJoinInfo entirely.
+	 */
+	foreach(l, root->join_info_list)
+	{
+		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
+
+		sjinfo->min_lefthand = bms_del_member(sjinfo->min_lefthand, relid);
+		sjinfo->min_righthand = bms_del_member(sjinfo->min_righthand, relid);
+		sjinfo->syn_lefthand = bms_del_member(sjinfo->syn_lefthand, relid);
+		sjinfo->syn_righthand = bms_del_member(sjinfo->syn_righthand, relid);
+	}
+
+	/*
+	 * Likewise remove references from PlaceHolderVar data structures,
+	 * removing any no-longer-needed placeholders entirely.
+	 *
+	 * Removal is a bit trickier than it might seem: we can remove PHVs that
+	 * are used at the target rel and/or in the join qual, but not those that
+	 * are used at join partner rels or above the join.  It's not that easy to
+	 * distinguish PHVs used at partner rels from those used in the join qual,
+	 * since they will both have ph_needed sets that are subsets of
+	 * joinrelids.  However, a PHV used at a partner rel could not have the
+	 * target rel in ph_eval_at, so we check that while deciding whether to
+	 * remove or just update the PHV.  There is no corresponding test in
+	 * join_is_removable because it doesn't need to distinguish those cases.
+	 */
+	foreach(l, root->placeholder_list)
+	{
+		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
+
+		Assert(!bms_is_member(relid, phinfo->ph_lateral));
+		if (bms_is_subset(phinfo->ph_needed, joinrelids) &&
+			bms_is_member(relid, phinfo->ph_eval_at))
+			root->placeholder_list = foreach_delete_current(root->placeholder_list,
+															l);
+		else
+		{
+			phinfo->ph_eval_at = bms_del_member(phinfo->ph_eval_at, relid);
+			Assert(!bms_is_empty(phinfo->ph_eval_at));
+			phinfo->ph_needed = bms_del_member(phinfo->ph_needed, relid);
+		}
+	}
+
+	/*
+	 * Remove any joinquals referencing the rel from the joininfo lists.
+	 *
+	 * In some cases, a joinqual has to be put back after deleting its
+	 * reference to the target rel.  This can occur for pseudoconstant and
+	 * outerjoin-delayed quals, which can get marked as requiring the rel in
+	 * order to force them to be evaluated at or above the join.  We can't
+	 * just discard them, though.  Only quals that logically belonged to the
+	 * outer join being discarded should be removed from the query.
+	 *
+	 * We must make a copy of the rel's old joininfo list before starting the
+	 * loop, because otherwise remove_join_clause_from_rels would destroy the
+	 * list while we're scanning it.
+	 */
+	joininfos = list_copy(rel->joininfo);
+	foreach(l, joininfos)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
+
+		remove_join_clause_from_rels(root, rinfo, rinfo->required_relids);
+
+		if (RINFO_IS_PUSHED_DOWN(rinfo, joinrelids))
+		{
+			/* Recheck that qual doesn't actually reference the target rel */
+			Assert(!bms_is_member(relid, rinfo->clause_relids));
+
+			/*
+			 * The required_relids probably aren't shared with anything else,
+			 * but let's copy them just to be sure.
+			 */
+			rinfo->required_relids = bms_copy(rinfo->required_relids);
+			rinfo->required_relids = bms_del_member(rinfo->required_relids,
+													relid);
+			distribute_restrictinfo_to_rels(root, rinfo);
+		}
+	}
+
+	/*
+	 * There may be references to the rel in root->fkey_list, but if so,
+	 * match_foreign_keys_to_quals() will get rid of them.
+	 */
+}
+
+/*
+ * Remove any occurrences of the target relid from a joinlist structure.
+ *
+ * It's easiest to build a whole new list structure, so we handle it that
+ * way.  Efficiency is not a big deal here.
+ *
+ * *nremoved is incremented by the number of occurrences removed (there
+ * should be exactly one, but the caller checks that).
+ */
+static List *
+remove_rel_from_joinlist(List *joinlist, int relid, int *nremoved)
+{
+	List	   *result = NIL;
+	ListCell   *jl;
+
+	foreach(jl, joinlist)
+	{
+		Node	   *jlnode = (Node *) lfirst(jl);
+
+		if (IsA(jlnode, RangeTblRef))
+		{
+			int			varno = ((RangeTblRef *) jlnode)->rtindex;
+
+			if (varno == relid)
+				(*nremoved)++;
+			else
+				result = lappend(result, jlnode);
+		}
+		else if (IsA(jlnode, List))
+		{
+			/* Recurse to handle subproblem */
+			List	   *sublist;
+
+			sublist = remove_rel_from_joinlist((List *) jlnode,
+											   relid, nremoved);
+			/* Avoid including empty sub-lists in the result */
+			if (sublist)
+				result = lappend(result, sublist);
+		}
+		else
+		{
+			elog(ERROR, "unrecognized joinlist node type: %d",
+				 (int) nodeTag(jlnode));
+		}
+	}
+
+	return result;
+}
+
+
+/*
+ * reduce_unique_semijoins
+ *		Check for semijoins that can be simplified to plain inner joins
+ *		because the inner relation is provably unique for the join clauses.
+ *
+ * Ideally this would happen during reduce_outer_joins, but we don't have
+ * enough information at that point.
+ *
+ * To perform the strength reduction when applicable, we need only delete
+ * the semijoin's SpecialJoinInfo from root->join_info_list.  (We don't
+ * bother fixing the join type attributed to it in the query jointree,
+ * since that won't be consulted again.)
+ */
+void
+reduce_unique_semijoins(PlannerInfo *root)
+{
+	ListCell   *lc;
+
+	/*
+	 * Scan the join_info_list to find semijoins.
+	 */
+	foreach(lc, root->join_info_list)
+	{
+		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
+		int			innerrelid;
+		RelOptInfo *innerrel;
+		Relids		joinrelids;
+		List	   *restrictlist;
+
+		/*
+		 * Must be a non-delaying semijoin to a single baserel, else we aren't
+		 * going to be able to do anything with it.  (It's probably not
+		 * possible for delay_upper_joins to be set on a semijoin, but we
+		 * might as well check.)
+		 */
+		if (sjinfo->jointype != JOIN_SEMI ||
+			sjinfo->delay_upper_joins)
+			continue;
+
+		if (!bms_get_singleton_member(sjinfo->min_righthand, &innerrelid))
+			continue;
+
+		innerrel = find_base_rel(root, innerrelid);
+
+		/*
+		 * Before we trouble to run generate_join_implied_equalities, make a
+		 * quick check to eliminate cases in which we will surely be unable to
+		 * prove uniqueness of the innerrel.
+		 */
+		if (!rel_supports_distinctness(root, innerrel))
+			continue;
+
+		/* Compute the relid set for the join we are considering */
+		joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
+
+		/*
+		 * Since we're only considering a single-rel RHS, any join clauses it
+		 * has must be clauses linking it to the semijoin's min_lefthand.  We
+		 * can also consider EC-derived join clauses.
+		 */
+		restrictlist =
+			list_concat(generate_join_implied_equalities(root,
+														 joinrelids,
+														 sjinfo->min_lefthand,
+														 innerrel),
+						innerrel->joininfo);
+
+		/* Test whether the innerrel is unique for those clauses. */
+		if (!innerrel_is_unique(root,
+								joinrelids, sjinfo->min_lefthand, innerrel,
+								JOIN_SEMI, restrictlist, true))
+			continue;
+
+		/* OK, remove the SpecialJoinInfo from the list. */
+		root->join_info_list = foreach_delete_current(root->join_info_list, lc);
+	}
+}
+
+
+/*
+ * rel_supports_distinctness
+ *		Could the relation possibly be proven distinct on some set of columns?
+ *
+ * This is effectively a pre-checking function for rel_is_distinct_for().
+ * It must return true if rel_is_distinct_for() could possibly return true
+ * with this rel, but it should not expend a lot of cycles.  The idea is
+ * that callers can avoid doing possibly-expensive processing to compute
+ * rel_is_distinct_for()'s argument lists if the call could not possibly
+ * succeed.
+ */
+static bool
+rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel)
+{
+	/* We only know about baserels ... */
+	if (rel->reloptkind != RELOPT_BASEREL)
+		return false;
+	if (rel->rtekind == RTE_RELATION)
+	{
+		/*
+		 * For a plain relation, we only know how to prove uniqueness by
+		 * reference to unique indexes.  Make sure there's at least one
+		 * suitable unique index.  It must be immediately enforced, and if
+		 * it's a partial index, it must match the query.  (Keep these
+		 * conditions in sync with relation_has_unique_index_for!)
+		 */
+		ListCell   *lc;
+
+		foreach(lc, rel->indexlist)
+		{
+			IndexOptInfo *ind = (IndexOptInfo *) lfirst(lc);
+
+			if (ind->unique && ind->immediate &&
+				(ind->indpred == NIL || ind->predOK))
+				return true;
+		}
+	}
+	else if (rel->rtekind == RTE_SUBQUERY)
+	{
+		Query	   *subquery = root->simple_rte_array[rel->relid]->subquery;
+
+		/* Check if the subquery has any qualities that support distinctness */
+		if (query_supports_distinctness(subquery))
+			return true;
+	}
+	/* We have no proof rules for any other rtekinds. */
+	return false;
+}
+
+/*
+ * rel_is_distinct_for
+ *		Does the relation return only distinct rows according to clause_list?
+ *
+ * clause_list is a list of join restriction clauses involving this rel and
+ * some other one.  Return true if no two rows emitted by this rel could
+ * possibly join to the same row of the other rel.
+ *
+ * The caller must have already determined that each condition is a
+ * mergejoinable equality with an expression in this relation on one side, and
+ * an expression not involving this relation on the other.  The transient
+ * outer_is_left flag is used to identify which side references this relation:
+ * left side if outer_is_left is false, right side if it is true.
+ *
+ * Note that the passed-in clause_list may be destructively modified!  This
+ * is OK for current uses, because the clause_list is built by the caller for
+ * the sole purpose of passing to this function.
+ */
+static bool
+rel_is_distinct_for(PlannerInfo *root, RelOptInfo *rel, List *clause_list)
+{
+	/*
+	 * We could skip a couple of tests here if we assume all callers checked
+	 * rel_supports_distinctness first, but it doesn't seem worth taking any
+	 * risk for.
+	 */
+	if (rel->reloptkind != RELOPT_BASEREL)
+		return false;
+	if (rel->rtekind == RTE_RELATION)
+	{
+		/*
+		 * Examine the indexes to see if we have a matching unique index.
+		 * relation_has_unique_index_for automatically adds any usable
+		 * restriction clauses for the rel, so we needn't do that here.
+		 */
+		if (relation_has_unique_index_for(root, rel, clause_list, NIL, NIL))
+			return true;
+	}
+	else if (rel->rtekind == RTE_SUBQUERY)
+	{
+		Index		relid = rel->relid;
+		Query	   *subquery = root->simple_rte_array[relid]->subquery;
+		List	   *colnos = NIL;
+		List	   *opids = NIL;
+		ListCell   *l;
+
+		/*
+		 * Build the argument lists for query_is_distinct_for: a list of
+		 * output column numbers that the query needs to be distinct over, and
+		 * a list of equality operators that the output columns need to be
+		 * distinct according to.
+		 *
+		 * (XXX we are not considering restriction clauses attached to the
+		 * subquery; is that worth doing?)
+		 */
+		foreach(l, clause_list)
+		{
+			RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);
+			Oid			op;
+			Var		   *var;
+
+			/*
+			 * Get the equality operator we need uniqueness according to.
+			 * (This might be a cross-type operator and thus not exactly the
+			 * same operator the subquery would consider; that's all right
+			 * since query_is_distinct_for can resolve such cases.)  The
+			 * caller's mergejoinability test should have selected only
+			 * OpExprs.
+			 */
+			op = castNode(OpExpr, rinfo->clause)->opno;
+
+			/* caller identified the inner side for us */
+			if (rinfo->outer_is_left)
+				var = (Var *) get_rightop(rinfo->clause);
+			else
+				var = (Var *) get_leftop(rinfo->clause);
+
+			/*
+			 * We may ignore any RelabelType node above the operand.  (There
+			 * won't be more than one, since eval_const_expressions() has been
+			 * applied already.)
+			 */
+			if (var && IsA(var, RelabelType))
+				var = (Var *) ((RelabelType *) var)->arg;
+
+			/*
+			 * If inner side isn't a Var referencing a subquery output column,
+			 * this clause doesn't help us.
+			 */
+			if (!var || !IsA(var, Var) ||
+				var->varno != relid || var->varlevelsup != 0)
+				continue;
+
+			colnos = lappend_int(colnos, var->varattno);
+			opids = lappend_oid(opids, op);
+		}
+
+		if (query_is_distinct_for(subquery, colnos, opids))
+			return true;
+	}
+	return false;
+}
+
+
+/*
+ * query_supports_distinctness - could the query possibly be proven distinct
+ *		on some set of output columns?
+ *
+ * This is effectively a pre-checking function for query_is_distinct_for().
+ * It must return true if query_is_distinct_for() could possibly return true
+ * with this query, but it should not expend a lot of cycles.  The idea is
+ * that callers can avoid doing possibly-expensive processing to compute
+ * query_is_distinct_for()'s argument lists if the call could not possibly
+ * succeed.
+ */
+bool
+query_supports_distinctness(Query *query)
+{
+	/* SRFs break distinctness except with DISTINCT, see below */
+	if (query->hasTargetSRFs && query->distinctClause == NIL)
+		return false;
+
+	/* check for features we can prove distinctness with */
+	if (query->distinctClause != NIL ||
+		query->groupClause != NIL ||
+		query->groupingSets != NIL ||
+		query->hasAggs ||
+		query->havingQual ||
+		query->setOperations)
+		return true;
+
+	return false;
+}
+
+/*
+ * query_is_distinct_for - does query never return duplicates of the
+ *		specified columns?
+ *
+ * query is a not-yet-planned subquery (in current usage, it's always from
+ * a subquery RTE, which the planner avoids scribbling on).
+ *
+ * colnos is an integer list of output column numbers (resno's).  We are
+ * interested in whether rows consisting of just these columns are certain
+ * to be distinct.  "Distinctness" is defined according to whether the
+ * corresponding upper-level equality operators listed in opids would think
+ * the values are distinct.  (Note: the opids entries could be cross-type
+ * operators, and thus not exactly the equality operators that the subquery
+ * would use itself.  We use equality_ops_are_compatible() to check
+ * compatibility.  That looks at btree or hash opfamily membership, and so
+ * should give trustworthy answers for all operators that we might need
+ * to deal with here.)
+ */
+bool
+query_is_distinct_for(Query *query, List *colnos, List *opids)
+{
+	ListCell   *l;
+	Oid			opid;
+
+	Assert(list_length(colnos) == list_length(opids));
+
+	/*
+	 * DISTINCT (including DISTINCT ON) guarantees uniqueness if all the
+	 * columns in the DISTINCT clause appear in colnos and operator semantics
+	 * match.  This is true even if there are SRFs in the DISTINCT columns or
+	 * elsewhere in the tlist.
+	 */
+	if (query->distinctClause)
+	{
+		foreach(l, query->distinctClause)
+		{
+			SortGroupClause *sgc = (SortGroupClause *) lfirst(l);
+			TargetEntry *tle = get_sortgroupclause_tle(sgc,
+													   query->targetList);
+
+			opid = distinct_col_search(tle->resno, colnos, opids);
+			if (!OidIsValid(opid) ||
+				!equality_ops_are_compatible(opid, sgc->eqop))
+				break;			/* exit early if no match */
+		}
+		if (l == NULL)			/* had matches for all? */
+			return true;
+	}
+
+	/*
+	 * Otherwise, a set-returning function in the query's targetlist can
+	 * result in returning duplicate rows, despite any grouping that might
+	 * occur before tlist evaluation.  (If all tlist SRFs are within GROUP BY
+	 * columns, it would be safe because they'd be expanded before grouping.
+	 * But it doesn't currently seem worth the effort to check for that.)
+	 */
+	if (query->hasTargetSRFs)
+		return false;
+
+	/*
+	 * Similarly, GROUP BY without GROUPING SETS guarantees uniqueness if all
+	 * the grouped columns appear in colnos and operator semantics match.
+	 */
+	if (query->groupClause && !query->groupingSets)
+	{
+		foreach(l, query->groupClause)
+		{
+			SortGroupClause *sgc = (SortGroupClause *) lfirst(l);
+			TargetEntry *tle = get_sortgroupclause_tle(sgc,
+													   query->targetList);
+
+			opid = distinct_col_search(tle->resno, colnos, opids);
+			if (!OidIsValid(opid) ||
+				!equality_ops_are_compatible(opid, sgc->eqop))
+				break;			/* exit early if no match */
+		}
+		if (l == NULL)			/* had matches for all? */
+			return true;
+	}
+	else if (query->groupingSets)
+	{
+		/*
+		 * If we have grouping sets with expressions, we probably don't have
+		 * uniqueness and analysis would be hard. Punt.
+		 */
+		if (query->groupClause)
+			return false;
+
+		/*
+		 * If we have no groupClause (therefore no grouping expressions), we
+		 * might have one or many empty grouping sets. If there's just one,
+		 * then we're returning only one row and are certainly unique. But
+		 * otherwise, we know we're certainly not unique.
+		 */
+		if (list_length(query->groupingSets) == 1 &&
+			((GroupingSet *) linitial(query->groupingSets))->kind == GROUPING_SET_EMPTY)
+			return true;
+		else
+			return false;
+	}
+	else
+	{
+		/*
+		 * If we have no GROUP BY, but do have aggregates or HAVING, then the
+		 * result is at most one row so it's surely unique, for any operators.
+		 */
+		if (query->hasAggs || query->havingQual)
+			return true;
+	}
+
+	/*
+	 * UNION, INTERSECT, EXCEPT guarantee uniqueness of the whole output row,
+	 * except with ALL.
+	 */
+	if (query->setOperations)
+	{
+		SetOperationStmt *topop = castNode(SetOperationStmt, query->setOperations);
+
+		Assert(topop->op != SETOP_NONE);
+
+		if (!topop->all)
+		{
+			ListCell   *lg;
+
+			/* We're good if all the nonjunk output columns are in colnos */
+			lg = list_head(topop->groupClauses);
+			foreach(l, query->targetList)
+			{
+				TargetEntry *tle = (TargetEntry *) lfirst(l);
+				SortGroupClause *sgc;
+
+				if (tle->resjunk)
+					continue;	/* ignore resjunk columns */
+
+				/* non-resjunk columns should have grouping clauses */
+				Assert(lg != NULL);
+				sgc = (SortGroupClause *) lfirst(lg);
+				lg = lnext(topop->groupClauses, lg);
+
+				opid = distinct_col_search(tle->resno, colnos, opids);
+				if (!OidIsValid(opid) ||
+					!equality_ops_are_compatible(opid, sgc->eqop))
+					break;		/* exit early if no match */
+			}
+			if (l == NULL)		/* had matches for all? */
+				return true;
+		}
+	}
+
+	/*
+	 * XXX Are there any other cases in which we can easily see the result
+	 * must be distinct?
+	 *
+	 * If you do add more smarts to this function, be sure to update
+	 * query_supports_distinctness() to match.
+	 */
+
+	return false;
+}
+
+/*
+ * distinct_col_search - subroutine for query_is_distinct_for
+ *
+ * If colno is in colnos, return the corresponding element of opids,
+ * else return InvalidOid.  (Ordinarily colnos would not contain duplicates,
+ * but if it does, we arbitrarily select the first match.)
+ */
+static Oid
+distinct_col_search(int colno, List *colnos, List *opids)
+{
+	ListCell   *lc1,
+			   *lc2;
+
+	forboth(lc1, colnos, lc2, opids)
+	{
+		if (colno == lfirst_int(lc1))
+			return lfirst_oid(lc2);
+	}
+	return InvalidOid;
+}
+
+
+/*
+ * innerrel_is_unique
+ *	  Check if the innerrel provably contains at most one tuple matching any
+ *	  tuple from the outerrel, based on join clauses in the 'restrictlist'.
+ *
+ * We need an actual RelOptInfo for the innerrel, but it's sufficient to
+ * identify the outerrel by its Relids.  This asymmetry supports use of this
+ * function before joinrels have been built.  (The caller is expected to
+ * also supply the joinrelids, just to save recalculating that.)
+ *
+ * The proof must be made based only on clauses that will be "joinquals"
+ * rather than "otherquals" at execution.  For an inner join there's no
+ * difference; but if the join is outer, we must ignore pushed-down quals,
+ * as those will become "otherquals".  Note that this means the answer might
+ * vary depending on whether IS_OUTER_JOIN(jointype); since we cache the
+ * answer without regard to that, callers must take care not to call this
+ * with jointypes that would be classified differently by IS_OUTER_JOIN().
+ *
+ * The actual proof is undertaken by is_innerrel_unique_for(); this function
+ * is a frontend that is mainly concerned with caching the answers.
+ * In particular, the force_cache argument allows overriding the internal
+ * heuristic about whether to cache negative answers; it should be "true"
+ * if making an inquiry that is not part of the normal bottom-up join search
+ * sequence.
+ */
+bool
+innerrel_is_unique(PlannerInfo *root,
+				   Relids joinrelids,
+				   Relids outerrelids,
+				   RelOptInfo *innerrel,
+				   JoinType jointype,
+				   List *restrictlist,
+				   bool force_cache)
+{
+	MemoryContext old_context;
+	ListCell   *lc;
+
+	/* Certainly can't prove uniqueness when there are no joinclauses */
+	if (restrictlist == NIL)
+		return false;
+
+	/*
+	 * Make a quick check to eliminate cases in which we will surely be unable
+	 * to prove uniqueness of the innerrel.
+	 */
+	if (!rel_supports_distinctness(root, innerrel))
+		return false;
+
+	/*
+	 * Query the cache to see if we've managed to prove that innerrel is
+	 * unique for any subset of this outerrel.  We don't need an exact match,
+	 * as extra outerrels can't make the innerrel any less unique (or more
+	 * formally, the restrictlist for a join to a superset outerrel must be a
+	 * superset of the conditions we successfully used before).
+	 */
+	foreach(lc, innerrel->unique_for_rels)
+	{
+		Relids		unique_for_rels = (Relids) lfirst(lc);
+
+		if (bms_is_subset(unique_for_rels, outerrelids))
+			return true;		/* Success! */
+	}
+
+	/*
+	 * Conversely, we may have already determined that this outerrel, or some
+	 * superset thereof, cannot prove this innerrel to be unique.
+	 */
+	foreach(lc, innerrel->non_unique_for_rels)
+	{
+		Relids		unique_for_rels = (Relids) lfirst(lc);
+
+		if (bms_is_subset(outerrelids, unique_for_rels))
+			return false;
+	}
+
+	/* No cached information, so try to make the proof. */
+	if (is_innerrel_unique_for(root, joinrelids, outerrelids, innerrel,
+							   jointype, restrictlist))
+	{
+		/*
+		 * Cache the positive result for future probes, being sure to keep it
+		 * in the planner_cxt even if we are working in GEQO.
+		 *
+		 * Note: one might consider trying to isolate the minimal subset of
+		 * the outerrels that proved the innerrel unique.  But it's not worth
+		 * the trouble, because the planner builds up joinrels incrementally
+		 * and so we'll see the minimally sufficient outerrels before any
+		 * supersets of them anyway.
+		 */
+		old_context = MemoryContextSwitchTo(root->planner_cxt);
+		innerrel->unique_for_rels = lappend(innerrel->unique_for_rels,
+											bms_copy(outerrelids));
+		MemoryContextSwitchTo(old_context);
+
+		return true;			/* Success! */
+	}
+	else
+	{
+		/*
+		 * None of the join conditions for outerrel proved innerrel unique, so
+		 * we can safely reject this outerrel or any subset of it in future
+		 * checks.
+		 *
+		 * However, in normal planning mode, caching this knowledge is totally
+		 * pointless; it won't be queried again, because we build up joinrels
+		 * from smaller to larger.  It is useful in GEQO mode, where the
+		 * knowledge can be carried across successive planning attempts; and
+		 * it's likely to be useful when using join-search plugins, too. Hence
+		 * cache when join_search_private is non-NULL.  (Yeah, that's a hack,
+		 * but it seems reasonable.)
+		 *
+		 * Also, allow callers to override that heuristic and force caching;
+		 * that's useful for reduce_unique_semijoins, which calls here before
+		 * the normal join search starts.
+		 */
+		if (force_cache || root->join_search_private)
+		{
+			old_context = MemoryContextSwitchTo(root->planner_cxt);
+			innerrel->non_unique_for_rels =
+				lappend(innerrel->non_unique_for_rels,
+						bms_copy(outerrelids));
+			MemoryContextSwitchTo(old_context);
+		}
+
+		return false;
+	}
+}
+
+/*
+ * is_innerrel_unique_for
+ *	  Check if the innerrel provably contains at most one tuple matching any
+ *	  tuple from the outerrel, based on join clauses in the 'restrictlist'.
+ */
+static bool
+is_innerrel_unique_for(PlannerInfo *root,
+					   Relids joinrelids,
+					   Relids outerrelids,
+					   RelOptInfo *innerrel,
+					   JoinType jointype,
+					   List *restrictlist)
+{
+	List	   *clause_list = NIL;
+	ListCell   *lc;
+
+	/*
+	 * Search for mergejoinable clauses that constrain the inner rel against
+	 * the outer rel.  If an operator is mergejoinable then it behaves like
+	 * equality for some btree opclass, so it's what we want.  The
+	 * mergejoinability test also eliminates clauses containing volatile
+	 * functions, which we couldn't depend on.
+	 */
+	foreach(lc, restrictlist)
+	{
+		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
+
+		/*
+		 * As noted above, if it's a pushed-down clause and we're at an outer
+		 * join, we can't use it.
+		 */
+		if (IS_OUTER_JOIN(jointype) &&
+			RINFO_IS_PUSHED_DOWN(restrictinfo, joinrelids))
+			continue;
+
+		/* Ignore if it's not a mergejoinable clause */
+		if (!restrictinfo->can_join ||
+			restrictinfo->mergeopfamilies == NIL)
+			continue;			/* not mergejoinable */
+
+		/*
+		 * Check if clause has the form "outer op inner" or "inner op outer",
+		 * and if so mark which side is inner.
+		 */
+		if (!clause_sides_match_join(restrictinfo, outerrelids,
+									 innerrel->relids))
+			continue;			/* no good for these input relations */
+
+		/* OK, add to list */
+		clause_list = lappend(clause_list, restrictinfo);
+	}
+
+	/* Let rel_is_distinct_for() do the hard work */
+	return rel_is_distinct_for(root, innerrel, clause_list);
+}