Fix representation of hash keys in Hash/HashJoin nodes.

In 5f32b29c I changed the creation of HashState.hashkeys to
actually use HashState as the parent (instead of HashJoinState, which
was incorrect, as they were executed below HashState), to fix the
problem of hashkeys expressions otherwise relying on slot types
appropriate for HashJoinState, rather than HashState as would be
correct. That reliance was only introduced in 12, which is why it
previously worked to use HashJoinState as the parent (although I'd be
unsurprised if there were problematic cases).

Unfortunately that's not a sufficient solution, because before this
commit, the to-be-hashed expressions referenced inner/outer as
appropriate for the HashJoin, not Hash. That didn't have obvious bad
consequences, because the slots containing the tuples were put into
ecxt_innertuple when hashing a tuple for HashState (even though Hash
doesn't have an inner plan).

There are less common cases where this can cause visible problems
however (rather than just confusion when inspecting such executor
trees). E.g. "ERROR: bogus varno: 65000", when explaining queries
containing a HashJoin where the subsidiary Hash node's hash keys
reference a subplan. While normally hashkeys aren't displayed by
EXPLAIN, if one of those expressions references a subplan, that
subplan may be printed as part of the Hash node - which then failed
because an inner plan was referenced, and Hash doesn't have that.

It seems quite possible that there's other broken cases, too.

Fix the problem by properly splitting the expression for the HashJoin
and Hash nodes at plan time, and have them reference the proper
subsidiary node. While other workarounds are possible, fixing this
correctly seems easy enough. It was a pretty ugly hack to have
ExecInitHashJoin put the expression into the already initialized
HashState, in the first place.

I decided to not just split inner/outer hashkeys inside
make_hashjoin(), but also to separate out hashoperators and
hashcollations at plan time. Otherwise we would have ended up having
two very similar loops, one at plan time and the other during executor
startup. The work seems to more appropriately belong to plan time,
anyway.

Reported-By: Nikita Glukhov, Alexander Korotkov
Author: Andres Freund
Reviewed-By: Tom Lane, in an earlier version
Discussion: https://postgr.es/m/CAPpHfdvGVegF_TKKRiBrSmatJL2dR9uwFCuR+teQ_8tEXU8mxg@mail.gmail.com
Backpatch: 12-

src/backend/executor/nodeHash.c

@@ -157,7 +157,8 @@ MultiExecPrivateHash(HashState *node)
 	econtext = node->ps.ps_ExprContext;
 
 	/*
-	 * get all inner tuples and insert into the hash table (or temp files)
+	 * Get all tuples from the node below the Hash node and insert into the
+	 * hash table (or temp files).
 	 */
 	for (;;)
 	{
@@ -165,7 +166,7 @@ MultiExecPrivateHash(HashState *node)
 		if (TupIsNull(slot))
 			break;
 		/* We have to compute the hash value */
-		econtext->ecxt_innertuple = slot;
+		econtext->ecxt_outertuple = slot;
 		if (ExecHashGetHashValue(hashtable, econtext, hashkeys,
 								 false, hashtable->keepNulls,
 								 &hashvalue))
@@ -281,7 +282,7 @@ MultiExecParallelHash(HashState *node)
 				slot = ExecProcNode(outerNode);
 				if (TupIsNull(slot))
 					break;
-				econtext->ecxt_innertuple = slot;
+				econtext->ecxt_outertuple = slot;
 				if (ExecHashGetHashValue(hashtable, econtext, hashkeys,
 										 false, hashtable->keepNulls,
 										 &hashvalue))
@@ -388,8 +389,9 @@ ExecInitHash(Hash *node, EState *estate, int eflags)
 	/*
 	 * initialize child expressions
 	 */
-	hashstate->ps.qual =
-		ExecInitQual(node->plan.qual, (PlanState *) hashstate);
+	Assert(node->plan.qual == NIL);
+	hashstate->hashkeys =
+		ExecInitExprList(node->hashkeys, (PlanState *) hashstate);
 
 	return hashstate;
 }
@@ -1773,9 +1775,13 @@ ExecParallelHashTableInsertCurrentBatch(HashJoinTable hashtable,
  * ExecHashGetHashValue
  *		Compute the hash value for a tuple
  *
- * The tuple to be tested must be in either econtext->ecxt_outertuple or
- * econtext->ecxt_innertuple.  Vars in the hashkeys expressions should have
- * varno either OUTER_VAR or INNER_VAR.
+ * The tuple to be tested must be in econtext->ecxt_outertuple (thus Vars in
+ * the hashkeys expressions need to have OUTER_VAR as varno). If outer_tuple
+ * is false (meaning it's the HashJoin's inner node, Hash), econtext,
+ * hashkeys, and slot need to be from Hash, with hashkeys/slot referencing and
+ * being suitable for tuples from the node below the Hash. Conversely, if
+ * outer_tuple is true, econtext is from HashJoin, and hashkeys/slot need to
+ * be appropriate for tuples from HashJoin's outer node.
  *
  * A true result means the tuple's hash value has been successfully computed
  * and stored at *hashvalue.  A false result means the tuple cannot match

src/backend/executor/nodeHashjoin.c

@@ -600,14 +600,8 @@ ExecInitHashJoin(HashJoin *node, EState *estate, int eflags)
 	HashJoinState *hjstate;
 	Plan	   *outerNode;
 	Hash	   *hashNode;
-	List	   *lclauses;
-	List	   *rclauses;
-	List	   *rhclauses;
-	List	   *hoperators;
-	List	   *hcollations;
 	TupleDesc	outerDesc,
 				innerDesc;
-	ListCell   *l;
 	const TupleTableSlotOps *ops;
 
 	/* check for unsupported flags */
@@ -730,36 +724,10 @@ ExecInitHashJoin(HashJoin *node, EState *estate, int eflags)
 	hjstate->hj_CurSkewBucketNo = INVALID_SKEW_BUCKET_NO;
 	hjstate->hj_CurTuple = NULL;
 
-	/*
-	 * Deconstruct the hash clauses into outer and inner argument values, so
-	 * that we can evaluate those subexpressions separately.  Also make a list
-	 * of the hash operator OIDs, in preparation for looking up the hash
-	 * functions to use.
-	 */
-	lclauses = NIL;
-	rclauses = NIL;
-	rhclauses = NIL;
-	hoperators = NIL;
-	hcollations = NIL;
-	foreach(l, node->hashclauses)
-	{
-		OpExpr	   *hclause = lfirst_node(OpExpr, l);
-
-		lclauses = lappend(lclauses, ExecInitExpr(linitial(hclause->args),
-												  (PlanState *) hjstate));
-		rclauses = lappend(rclauses, ExecInitExpr(lsecond(hclause->args),
-												  (PlanState *) hjstate));
-		rhclauses = lappend(rhclauses, ExecInitExpr(lsecond(hclause->args),
-													innerPlanState(hjstate)));
-		hoperators = lappend_oid(hoperators, hclause->opno);
-		hcollations = lappend_oid(hcollations, hclause->inputcollid);
-	}
-	hjstate->hj_OuterHashKeys = lclauses;
-	hjstate->hj_InnerHashKeys = rclauses;
-	hjstate->hj_HashOperators = hoperators;
-	hjstate->hj_Collations = hcollations;
-	/* child Hash node needs to evaluate inner hash keys, too */
-	((HashState *) innerPlanState(hjstate))->hashkeys = rhclauses;
+	hjstate->hj_OuterHashKeys = ExecInitExprList(node->hashkeys,
+												 (PlanState *) hjstate);
+	hjstate->hj_HashOperators = node->hashoperators;
+	hjstate->hj_Collations = node->hashcollations;
 
 	hjstate->hj_JoinState = HJ_BUILD_HASHTABLE;
 	hjstate->hj_MatchedOuter = false;

src/backend/nodes/copyfuncs.c

@@ -899,6 +899,9 @@ _copyHashJoin(const HashJoin *from)
 	 * copy remainder of node
 	 */
 	COPY_NODE_FIELD(hashclauses);
+	COPY_NODE_FIELD(hashoperators);
+	COPY_NODE_FIELD(hashcollations);
+	COPY_NODE_FIELD(hashkeys);
 
 	return newnode;
 }
@@ -1066,6 +1069,7 @@ _copyHash(const Hash *from)
 	/*
 	 * copy remainder of node
 	 */
+	COPY_NODE_FIELD(hashkeys);
 	COPY_SCALAR_FIELD(skewTable);
 	COPY_SCALAR_FIELD(skewColumn);
 	COPY_SCALAR_FIELD(skewInherit);

src/backend/nodes/outfuncs.c

@@ -761,6 +761,9 @@ _outHashJoin(StringInfo str, const HashJoin *node)
 	_outJoinPlanInfo(str, (const Join *) node);
 
 	WRITE_NODE_FIELD(hashclauses);
+	WRITE_NODE_FIELD(hashoperators);
+	WRITE_NODE_FIELD(hashcollations);
+	WRITE_NODE_FIELD(hashkeys);
 }
 
 static void
@@ -863,6 +866,7 @@ _outHash(StringInfo str, const Hash *node)
 
 	_outPlanInfo(str, (const Plan *) node);
 
+	WRITE_NODE_FIELD(hashkeys);
 	WRITE_OID_FIELD(skewTable);
 	WRITE_INT_FIELD(skewColumn);
 	WRITE_BOOL_FIELD(skewInherit);

src/backend/nodes/readfuncs.c

@@ -2096,6 +2096,9 @@ _readHashJoin(void)
 	ReadCommonJoin(&local_node->join);
 
 	READ_NODE_FIELD(hashclauses);
+	READ_NODE_FIELD(hashoperators);
+	READ_NODE_FIELD(hashcollations);
+	READ_NODE_FIELD(hashkeys);
 
 	READ_DONE();
 }
@@ -2274,6 +2277,7 @@ _readHash(void)
 
 	ReadCommonPlan(&local_node->plan);
 
+	READ_NODE_FIELD(hashkeys);
 	READ_OID_FIELD(skewTable);
 	READ_INT_FIELD(skewColumn);
 	READ_BOOL_FIELD(skewInherit);

src/backend/optimizer/plan/createplan.c

@@ -222,9 +222,12 @@ static NestLoop *make_nestloop(List *tlist,
 static HashJoin *make_hashjoin(List *tlist,
 							   List *joinclauses, List *otherclauses,
 							   List *hashclauses,
+							   List *hashoperators, List *hashcollations,
+							   List *hashkeys,
 							   Plan *lefttree, Plan *righttree,
 							   JoinType jointype, bool inner_unique);
 static Hash *make_hash(Plan *lefttree,
+					   List *hashkeys,
 					   Oid skewTable,
 					   AttrNumber skewColumn,
 					   bool skewInherit);
@@ -4380,9 +4383,14 @@ create_hashjoin_plan(PlannerInfo *root,
 	List	   *joinclauses;
 	List	   *otherclauses;
 	List	   *hashclauses;
+	List	   *hashoperators = NIL;
+	List	   *hashcollations = NIL;
+	List	   *inner_hashkeys = NIL;
+	List	   *outer_hashkeys = NIL;
 	Oid			skewTable = InvalidOid;
 	AttrNumber	skewColumn = InvalidAttrNumber;
 	bool		skewInherit = false;
+	ListCell   *lc;
 
 	/*
 	 * HashJoin can project, so we don't have to demand exact tlists from the
@@ -4474,10 +4482,29 @@ create_hashjoin_plan(PlannerInfo *root,
 		}
 	}
 
+	/*
+	 * Collect hash related information. The hashed expressions are
+	 * deconstructed into outer/inner expressions, so they can be computed
+	 * separately (inner expressions are used to build the hashtable via Hash,
+	 * outer expressions to perform lookups of tuples from HashJoin's outer
+	 * plan in the hashtable). Also collect operator information necessary to
+	 * build the hashtable.
+	 */
+	foreach(lc, hashclauses)
+	{
+		OpExpr	   *hclause = lfirst_node(OpExpr, lc);
+
+		hashoperators = lappend_oid(hashoperators, hclause->opno);
+		hashcollations = lappend_oid(hashcollations, hclause->inputcollid);
+		outer_hashkeys = lappend(outer_hashkeys, linitial(hclause->args));
+		inner_hashkeys = lappend(inner_hashkeys, lsecond(hclause->args));
+	}
+
 	/*
 	 * Build the hash node and hash join node.
 	 */
 	hash_plan = make_hash(inner_plan,
+						  inner_hashkeys,
 						  skewTable,
 						  skewColumn,
 						  skewInherit);
@@ -4504,6 +4531,9 @@ create_hashjoin_plan(PlannerInfo *root,
 							  joinclauses,
 							  otherclauses,
 							  hashclauses,
+							  hashoperators,
+							  hashcollations,
+							  outer_hashkeys,
 							  outer_plan,
 							  (Plan *) hash_plan,
 							  best_path->jpath.jointype,
@@ -5545,6 +5575,9 @@ make_hashjoin(List *tlist,
 			  List *joinclauses,
 			  List *otherclauses,
 			  List *hashclauses,
+			  List *hashoperators,
+			  List *hashcollations,
+			  List *hashkeys,
 			  Plan *lefttree,
 			  Plan *righttree,
 			  JoinType jointype,
@@ -5558,6 +5591,9 @@ make_hashjoin(List *tlist,
 	plan->lefttree = lefttree;
 	plan->righttree = righttree;
 	node->hashclauses = hashclauses;
+	node->hashoperators = hashoperators;
+	node->hashcollations = hashcollations;
+	node->hashkeys = hashkeys;
 	node->join.jointype = jointype;
 	node->join.inner_unique = inner_unique;
 	node->join.joinqual = joinclauses;
@@ -5567,6 +5603,7 @@ make_hashjoin(List *tlist,
 
 static Hash *
 make_hash(Plan *lefttree,
+		  List *hashkeys,
 		  Oid skewTable,
 		  AttrNumber skewColumn,
 		  bool skewInherit)
@@ -5579,6 +5616,7 @@ make_hash(Plan *lefttree,
 	plan->lefttree = lefttree;
 	plan->righttree = NULL;
 
+	node->hashkeys = hashkeys;
 	node->skewTable = skewTable;
 	node->skewColumn = skewColumn;
 	node->skewInherit = skewInherit;

src/backend/optimizer/plan/setrefs.c

@@ -107,6 +107,7 @@ static Plan *set_append_references(PlannerInfo *root,
 static Plan *set_mergeappend_references(PlannerInfo *root,
 										MergeAppend *mplan,
 										int rtoffset);
+static void set_hash_references(PlannerInfo *root, Plan *plan, int rtoffset);
 static Node *fix_scan_expr(PlannerInfo *root, Node *node, int rtoffset);
 static Node *fix_scan_expr_mutator(Node *node, fix_scan_expr_context *context);
 static bool fix_scan_expr_walker(Node *node, fix_scan_expr_context *context);
@@ -646,6 +647,9 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 			break;
 
 		case T_Hash:
+			set_hash_references(root, plan, rtoffset);
+			break;
+
 		case T_Material:
 		case T_Sort:
 		case T_Unique:
@@ -1419,6 +1423,36 @@ set_mergeappend_references(PlannerInfo *root,
 	return (Plan *) mplan;
 }
 
+/*
+ * set_hash_references
+ *	   Do set_plan_references processing on a Hash node
+ */
+static void
+set_hash_references(PlannerInfo *root, Plan *plan, int rtoffset)
+{
+	Hash	   *hplan = (Hash *) plan;
+	Plan	   *outer_plan = plan->lefttree;
+	indexed_tlist *outer_itlist;
+
+	/*
+	 * Hash's hashkeys are used when feeding tuples into the hashtable,
+	 * therefore have them reference Hash's outer plan (which itself is the
+	 * inner plan of the HashJoin).
+	 */
+	outer_itlist = build_tlist_index(outer_plan->targetlist);
+	hplan->hashkeys = (List *)
+		fix_upper_expr(root,
+					   (Node *) hplan->hashkeys,
+					   outer_itlist,
+					   OUTER_VAR,
+					   rtoffset);
+
+	/* Hash doesn't project */
+	set_dummy_tlist_references(plan, rtoffset);
+
+	/* Hash nodes don't have their own quals */
+	Assert(plan->qual == NIL);
+}
 
 /*
  * copyVar
@@ -1754,6 +1788,16 @@ set_join_references(PlannerInfo *root, Join *join, int rtoffset)
 										inner_itlist,
 										(Index) 0,
 										rtoffset);
+
+		/*
+		 * HashJoin's hashkeys are used to look for matching tuples from its
+		 * outer plan (not the Hash node!) in the hashtable.
+		 */
+		hj->hashkeys = (List *) fix_upper_expr(root,
+											   (Node *) hj->hashkeys,
+											   outer_itlist,
+											   OUTER_VAR,
+											   rtoffset);
 	}
 
 	/*

src/include/nodes/execnodes.h

@@ -1852,7 +1852,6 @@ typedef struct MergeJoinState
  *
  *		hashclauses				original form of the hashjoin condition
  *		hj_OuterHashKeys		the outer hash keys in the hashjoin condition
- *		hj_InnerHashKeys		the inner hash keys in the hashjoin condition
  *		hj_HashOperators		the join operators in the hashjoin condition
  *		hj_HashTable			hash table for the hashjoin
  *								(NULL if table not built yet)
@@ -1883,7 +1882,6 @@ typedef struct HashJoinState
 	JoinState	js;				/* its first field is NodeTag */
 	ExprState  *hashclauses;
 	List	   *hj_OuterHashKeys;	/* list of ExprState nodes */
-	List	   *hj_InnerHashKeys;	/* list of ExprState nodes */
 	List	   *hj_HashOperators;	/* list of operator OIDs */
 	List	   *hj_Collations;
 	HashJoinTable hj_HashTable;
@@ -2222,7 +2220,6 @@ typedef struct HashState
 	PlanState	ps;				/* its first field is NodeTag */
 	HashJoinTable hashtable;	/* hash table for the hashjoin */
 	List	   *hashkeys;		/* list of ExprState nodes */
-	/* hashkeys is same as parent's hj_InnerHashKeys */
 
 	SharedHashInfo *shared_info;	/* one entry per worker */
 	HashInstrumentation *hinstrument;	/* this worker's entry */

src/include/nodes/plannodes.h

@@ -737,6 +737,14 @@ typedef struct HashJoin
 {
 	Join		join;
 	List	   *hashclauses;
+	List	   *hashoperators;
+	List	   *hashcollations;
+
+	/*
+	 * List of expressions to be hashed for tuples from the outer plan, to
+	 * perform lookups in the hashtable over the inner plan.
+	 */
+	List	   *hashkeys;
 } HashJoin;
 
 /* ----------------
@@ -899,6 +907,12 @@ typedef struct GatherMerge
 typedef struct Hash
 {
 	Plan		plan;
+
+	/*
+	 * List of expressions to be hashed for tuples from Hash's outer plan,
+	 * needed to put them into the hashtable.
+	 */
+	List	   *hashkeys;		/* hash keys for the hashjoin condition */
 	Oid			skewTable;		/* outer join key's table OID, or InvalidOid */
 	AttrNumber	skewColumn;		/* outer join key's column #, or zero */
 	bool		skewInherit;	/* is outer join rel an inheritance tree? */

src/test/regress/expected/join_hash.out

@@ -879,3 +879,137 @@ $$);
 
 rollback to settings;
 rollback;
+-- Verify that hash key expressions reference the correct
+-- nodes. Hashjoin's hashkeys need to reference its outer plan, Hash's
+-- need to reference Hash's outer plan (which is below HashJoin's
+-- inner plan). It's not trivial to verify that the references are
+-- correct (we don't display the hashkeys themselves), but if the
+-- hashkeys contain subplan references, those will be displayed. Force
+-- subplans to appear just about everywhere.
+--
+-- Bug report:
+-- https://www.postgresql.org/message-id/CAPpHfdvGVegF_TKKRiBrSmatJL2dR9uwFCuR%2BteQ_8tEXU8mxg%40mail.gmail.com
+--
+BEGIN;
+SET LOCAL enable_sort = OFF; -- avoid mergejoins
+SET LOCAL from_collapse_limit = 1; -- allows easy changing of join order
+CREATE TABLE hjtest_1 (a text, b int, id int, c bool);
+CREATE TABLE hjtest_2 (a bool, id int, b text, c int);
+INSERT INTO hjtest_1(a, b, id, c) VALUES ('text', 2, 1, false); -- matches
+INSERT INTO hjtest_1(a, b, id, c) VALUES ('text', 1, 2, false); -- fails id join condition
+INSERT INTO hjtest_1(a, b, id, c) VALUES ('text', 20, 1, false); -- fails < 50
+INSERT INTO hjtest_1(a, b, id, c) VALUES ('text', 1, 1, false); -- fails (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 1, 'another', 2); -- matches
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 3, 'another', 7); -- fails id join condition
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 1, 'another', 90);  -- fails < 55
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 1, 'another', 3); -- fails (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 1, 'text', 1); --  fails hjtest_1.a <> hjtest_2.b;
+EXPLAIN (COSTS OFF, VERBOSE)
+SELECT hjtest_1.a a1, hjtest_2.a a2,hjtest_1.tableoid::regclass t1, hjtest_2.tableoid::regclass t2
+FROM hjtest_1, hjtest_2
+WHERE
+    hjtest_1.id = (SELECT 1 WHERE hjtest_2.id = 1)
+    AND (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+    AND (SELECT hjtest_1.b * 5) < 50
+    AND (SELECT hjtest_2.c * 5) < 55
+    AND hjtest_1.a <> hjtest_2.b;
+                                           QUERY PLAN                                           
+------------------------------------------------------------------------------------------------
+ Hash Join
+   Output: hjtest_1.a, hjtest_2.a, (hjtest_1.tableoid)::regclass, (hjtest_2.tableoid)::regclass
+   Hash Cond: ((hjtest_1.id = (SubPlan 1)) AND ((SubPlan 2) = (SubPlan 3)))
+   Join Filter: (hjtest_1.a <> hjtest_2.b)
+   ->  Seq Scan on public.hjtest_1
+         Output: hjtest_1.a, hjtest_1.tableoid, hjtest_1.id, hjtest_1.b
+         Filter: ((SubPlan 4) < 50)
+         SubPlan 4
+           ->  Result
+                 Output: (hjtest_1.b * 5)
+   ->  Hash
+         Output: hjtest_2.a, hjtest_2.tableoid, hjtest_2.id, hjtest_2.c, hjtest_2.b
+         ->  Seq Scan on public.hjtest_2
+               Output: hjtest_2.a, hjtest_2.tableoid, hjtest_2.id, hjtest_2.c, hjtest_2.b
+               Filter: ((SubPlan 5) < 55)
+               SubPlan 5
+                 ->  Result
+                       Output: (hjtest_2.c * 5)
+         SubPlan 1
+           ->  Result
+                 Output: 1
+                 One-Time Filter: (hjtest_2.id = 1)
+         SubPlan 3
+           ->  Result
+                 Output: (hjtest_2.c * 5)
+   SubPlan 2
+     ->  Result
+           Output: (hjtest_1.b * 5)
+(28 rows)
+
+SELECT hjtest_1.a a1, hjtest_2.a a2,hjtest_1.tableoid::regclass t1, hjtest_2.tableoid::regclass t2
+FROM hjtest_1, hjtest_2
+WHERE
+    hjtest_1.id = (SELECT 1 WHERE hjtest_2.id = 1)
+    AND (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+    AND (SELECT hjtest_1.b * 5) < 50
+    AND (SELECT hjtest_2.c * 5) < 55
+    AND hjtest_1.a <> hjtest_2.b;
+  a1  | a2 |    t1    |    t2    
+------+----+----------+----------
+ text | t  | hjtest_1 | hjtest_2
+(1 row)
+
+EXPLAIN (COSTS OFF, VERBOSE)
+SELECT hjtest_1.a a1, hjtest_2.a a2,hjtest_1.tableoid::regclass t1, hjtest_2.tableoid::regclass t2
+FROM hjtest_2, hjtest_1
+WHERE
+    hjtest_1.id = (SELECT 1 WHERE hjtest_2.id = 1)
+    AND (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+    AND (SELECT hjtest_1.b * 5) < 50
+    AND (SELECT hjtest_2.c * 5) < 55
+    AND hjtest_1.a <> hjtest_2.b;
+                                           QUERY PLAN                                           
+------------------------------------------------------------------------------------------------
+ Hash Join
+   Output: hjtest_1.a, hjtest_2.a, (hjtest_1.tableoid)::regclass, (hjtest_2.tableoid)::regclass
+   Hash Cond: (((SubPlan 1) = hjtest_1.id) AND ((SubPlan 3) = (SubPlan 2)))
+   Join Filter: (hjtest_1.a <> hjtest_2.b)
+   ->  Seq Scan on public.hjtest_2
+         Output: hjtest_2.a, hjtest_2.tableoid, hjtest_2.id, hjtest_2.c, hjtest_2.b
+         Filter: ((SubPlan 5) < 55)
+         SubPlan 5
+           ->  Result
+                 Output: (hjtest_2.c * 5)
+   ->  Hash
+         Output: hjtest_1.a, hjtest_1.tableoid, hjtest_1.id, hjtest_1.b
+         ->  Seq Scan on public.hjtest_1
+               Output: hjtest_1.a, hjtest_1.tableoid, hjtest_1.id, hjtest_1.b
+               Filter: ((SubPlan 4) < 50)
+               SubPlan 4
+                 ->  Result
+                       Output: (hjtest_1.b * 5)
+         SubPlan 2
+           ->  Result
+                 Output: (hjtest_1.b * 5)
+   SubPlan 1
+     ->  Result
+           Output: 1
+           One-Time Filter: (hjtest_2.id = 1)
+   SubPlan 3
+     ->  Result
+           Output: (hjtest_2.c * 5)
+(28 rows)
+
+SELECT hjtest_1.a a1, hjtest_2.a a2,hjtest_1.tableoid::regclass t1, hjtest_2.tableoid::regclass t2
+FROM hjtest_2, hjtest_1
+WHERE
+    hjtest_1.id = (SELECT 1 WHERE hjtest_2.id = 1)
+    AND (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+    AND (SELECT hjtest_1.b * 5) < 50
+    AND (SELECT hjtest_2.c * 5) < 55
+    AND hjtest_1.a <> hjtest_2.b;
+  a1  | a2 |    t1    |    t2    
+------+----+----------+----------
+ text | t  | hjtest_1 | hjtest_2
+(1 row)
+
+ROLLBACK;

src/test/regress/sql/join_hash.sql

@@ -468,3 +468,73 @@ $$);
 rollback to settings;
 
 rollback;
+
+
+-- Verify that hash key expressions reference the correct
+-- nodes. Hashjoin's hashkeys need to reference its outer plan, Hash's
+-- need to reference Hash's outer plan (which is below HashJoin's
+-- inner plan). It's not trivial to verify that the references are
+-- correct (we don't display the hashkeys themselves), but if the
+-- hashkeys contain subplan references, those will be displayed. Force
+-- subplans to appear just about everywhere.
+--
+-- Bug report:
+-- https://www.postgresql.org/message-id/CAPpHfdvGVegF_TKKRiBrSmatJL2dR9uwFCuR%2BteQ_8tEXU8mxg%40mail.gmail.com
+--
+BEGIN;
+SET LOCAL enable_sort = OFF; -- avoid mergejoins
+SET LOCAL from_collapse_limit = 1; -- allows easy changing of join order
+
+CREATE TABLE hjtest_1 (a text, b int, id int, c bool);
+CREATE TABLE hjtest_2 (a bool, id int, b text, c int);
+
+INSERT INTO hjtest_1(a, b, id, c) VALUES ('text', 2, 1, false); -- matches
+INSERT INTO hjtest_1(a, b, id, c) VALUES ('text', 1, 2, false); -- fails id join condition
+INSERT INTO hjtest_1(a, b, id, c) VALUES ('text', 20, 1, false); -- fails < 50
+INSERT INTO hjtest_1(a, b, id, c) VALUES ('text', 1, 1, false); -- fails (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 1, 'another', 2); -- matches
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 3, 'another', 7); -- fails id join condition
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 1, 'another', 90);  -- fails < 55
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 1, 'another', 3); -- fails (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+INSERT INTO hjtest_2(a, id, b, c) VALUES (true, 1, 'text', 1); --  fails hjtest_1.a <> hjtest_2.b;
+
+EXPLAIN (COSTS OFF, VERBOSE)
+SELECT hjtest_1.a a1, hjtest_2.a a2,hjtest_1.tableoid::regclass t1, hjtest_2.tableoid::regclass t2
+FROM hjtest_1, hjtest_2
+WHERE
+    hjtest_1.id = (SELECT 1 WHERE hjtest_2.id = 1)
+    AND (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+    AND (SELECT hjtest_1.b * 5) < 50
+    AND (SELECT hjtest_2.c * 5) < 55
+    AND hjtest_1.a <> hjtest_2.b;
+
+SELECT hjtest_1.a a1, hjtest_2.a a2,hjtest_1.tableoid::regclass t1, hjtest_2.tableoid::regclass t2
+FROM hjtest_1, hjtest_2
+WHERE
+    hjtest_1.id = (SELECT 1 WHERE hjtest_2.id = 1)
+    AND (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+    AND (SELECT hjtest_1.b * 5) < 50
+    AND (SELECT hjtest_2.c * 5) < 55
+    AND hjtest_1.a <> hjtest_2.b;
+
+EXPLAIN (COSTS OFF, VERBOSE)
+SELECT hjtest_1.a a1, hjtest_2.a a2,hjtest_1.tableoid::regclass t1, hjtest_2.tableoid::regclass t2
+FROM hjtest_2, hjtest_1
+WHERE
+    hjtest_1.id = (SELECT 1 WHERE hjtest_2.id = 1)
+    AND (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+    AND (SELECT hjtest_1.b * 5) < 50
+    AND (SELECT hjtest_2.c * 5) < 55
+    AND hjtest_1.a <> hjtest_2.b;
+
+SELECT hjtest_1.a a1, hjtest_2.a a2,hjtest_1.tableoid::regclass t1, hjtest_2.tableoid::regclass t2
+FROM hjtest_2, hjtest_1
+WHERE
+    hjtest_1.id = (SELECT 1 WHERE hjtest_2.id = 1)
+    AND (SELECT hjtest_1.b * 5) = (SELECT hjtest_2.c*5)
+    AND (SELECT hjtest_1.b * 5) < 50
+    AND (SELECT hjtest_2.c * 5) < 55
+    AND hjtest_1.a <> hjtest_2.b;
+
+ROLLBACK;