Implement UPDATE tab SET (col1,col2,...) = (SELECT ...), ...

This SQL-standard feature allows a sub-SELECT yielding multiple columns (but only one row) to be used to compute the new values of several columns to be updated. While the same results can be had with an independent sub-SELECT per column, such a workaround can require a great deal of duplicated computation. The standard actually says that the source for a multi-column assignment could be any row-valued expression. The implementation used here is tightly tied to our existing sub-SELECT support and can't handle other cases; the Bison grammar would have some issues with them too. However, I don't feel too bad about this since other cases can be converted into sub-SELECTs. For instance, "SET (a,b,c) = row_valued_function(x)" could be written "SET (a,b,c) = (SELECT * FROM row_valued_function(x))".
11 years ago · 8f889b1083
parent 230ba02d85
commit 8f889b1083
31 changed files with 805 additions and 122 deletions
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@ -2396,6 +2396,7 @@ JumbleExpr(pgssJumbleState *jstate, Node *node)
 				SubLink    *sublink = (SubLink *) node;
 				APP_JUMB(sublink->subLinkType);
 				APP_JUMB(sublink->subLinkId);
 				JumbleExpr(jstate, (Node *) sublink->testexpr);
 				JumbleQuery(jstate, (Query *) sublink->subselect);
 			}
--- a/doc/src/sgml/ref/update.sgml
+++ b/doc/src/sgml/ref/update.sgml
@ -24,7 +24,9 @@ PostgreSQL documentation
 [ WITH [ RECURSIVE ] <replaceable class="parameter">with_query</replaceable> [, ...] ]
 UPDATE [ ONLY ] <replaceable class="PARAMETER">table_name</replaceable> [ * ] [ [ AS ] <replaceable class="parameter">alias</replaceable> ]
    SET { <replaceable class="PARAMETER">column_name</replaceable> = { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } |
-          ( <replaceable class="PARAMETER">column_name</replaceable> [, ...] ) = ( { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] ) } [, ...]
+          ( <replaceable class="PARAMETER">column_name</replaceable> [, ...] ) = ( { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] ) |
          ( <replaceable class="PARAMETER">column_name</replaceable> [, ...] ) = ( <replaceable class="PARAMETER">sub-SELECT</replaceable> )
        } [, ...]
    [ FROM <replaceable class="PARAMETER">from_list</replaceable> ]
    [ WHERE <replaceable class="PARAMETER">condition</replaceable> | WHERE CURRENT OF <replaceable class="PARAMETER">cursor_name</replaceable> ]
    [ RETURNING * | <replaceable class="parameter">output_expression</replaceable> [ [ AS ] <replaceable class="parameter">output_name</replaceable> ] [, ...] ]
@ -146,6 +148,21 @@ UPDATE [ ONLY ] <replaceable class="PARAMETER">table_name</replaceable> [ * ] [
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><replaceable class="PARAMETER">sub-SELECT</replaceable></term>
    <listitem>
     <para>
      A <literal>SELECT</> sub-query that produces as many output columns
      as are listed in the parenthesized column list preceding it.  The
      sub-query must yield no more than one row when executed.  If it
      yields one row, its column values are assigned to the target columns;
      if it yields no rows, NULL values are assigned to the target columns.
      The sub-query can refer to old values of the current row of the table
      being updated.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><replaceable class="PARAMETER">from_list</replaceable></term>
    <listitem>
@ -324,6 +341,38 @@ UPDATE employees SET sales_count = sales_count + 1 WHERE id =
 </programlisting>
  </para>
  <para>
   Update contact names in an accounts table to match the currently assigned
   salesmen:
 <programlisting>
 UPDATE accounts SET (contact_first_name, contact_last_name) =
    (SELECT first_name, last_name FROM salesmen
     WHERE salesmen.id = accounts.sales_id);
 </programlisting>
   A similar result could be accomplished with a join:
 <programlisting>
 UPDATE accounts SET contact_first_name = first_name,
                    contact_last_name = last_name
  FROM salesmen WHERE salesmen.id = accounts.sales_id;
 </programlisting>
   However, the second query may give unexpected results
   if <structname>salesmen</>.<structfield>id</> is not a unique key, whereas
   the first query is guaranteed to raise an error if there are multiple
   <structfield>id</> matches.  Also, if there is no match for a particular
   <structname>accounts</>.<structfield>sales_id</> entry, the first query
   will set the corresponding name fields to NULL, whereas the second query
   will not update that row at all.
  </para>
  <para>
   Update statistics in a summary table to match the current data:
 <programlisting>
 UPDATE summary s SET (sum_x, sum_y, avg_x, avg_y) =
    (SELECT sum(x), sum(y), avg(x), avg(y) FROM data d
     WHERE d.group_id = s.group_id);
 </programlisting>
  </para>
  <para>
   Attempt to insert a new stock item along with the quantity of stock. If
   the item already exists, instead update the stock count of the existing
@ -361,19 +410,6 @@ UPDATE films SET kind = 'Dramatic' WHERE CURRENT OF c_films;
   to use <literal>WITH</> with <command>UPDATE</>.
  </para>
  <para>
   According to the standard, the column-list syntax should allow a list
   of columns to be assigned from a single row-valued expression, such
   as a sub-select:
 <programlisting>
 UPDATE accounts SET (contact_last_name, contact_first_name) =
    (SELECT last_name, first_name FROM salesmen
     WHERE salesmen.id = accounts.sales_id);
 </programlisting>
   This is not currently implemented &mdash; the source must be a list
   of independent expressions.
  </para>
  <para>
   Some other database systems offer a <literal>FROM</> option in which
   the target table is supposed to be listed again within <literal>FROM</>.
@ -381,5 +417,15 @@ UPDATE accounts SET (contact_last_name, contact_first_name) =
   <literal>FROM</>.  Be careful when porting applications that use this
   extension.
  </para>
  <para>
   According to the standard, the source value for a parenthesized sub-list of
   column names can be any row-valued expression yielding the correct number
   of columns.  <productname>PostgreSQL</productname> only allows the source
   value to be a parenthesized list of expressions (a row constructor) or a
   sub-<literal>SELECT</>.  An individual column's updated value can be
   specified as <literal>DEFAULT</> in the row-constructor case, but not
   inside a sub-<literal>SELECT</>.
  </para>
 </refsect1>
 </refentry>
--- a/doc/src/sgml/rules.sgml
+++ b/doc/src/sgml/rules.sgml
@ -1164,6 +1164,27 @@ SELECT word FROM words ORDER BY word <-> 'caterpiler' LIMIT 10;
    original one.
 </para>
 <caution>
 <para>
  In many cases, tasks that could be performed by rules
  on <command>INSERT</>/<command>UPDATE</>/<command>DELETE</> are better done
  with triggers.  Triggers are notationally a bit more complicated, but their
  semantics are much simpler to understand.  Rules tend to have surprising
  results when the original query contains volatile functions: volatile
  functions may get executed more times than expected in the process of
  carrying out the rules.
 </para>
 <para>
  Also, there are some cases that are not supported by these types of rules at
  all, notably including <literal>WITH</> clauses in the original query and
  multiple-assignment sub-<literal>SELECT</>s in the <literal>SET</> list
  of <command>UPDATE</> queries.  This is because copying these constructs
  into a rule query would result in multiple evaluations of the sub-query,
  contrary to the express intent of the query's author.
 </para>
 </caution>
 <sect2>
 <title>How Update Rules Work</title>
--- a/src/backend/executor/nodeSubplan.c
+++ b/src/backend/executor/nodeSubplan.c
@ -1,7 +1,15 @@
 /*-------------------------------------------------------------------------
 *
 * nodeSubplan.c
- *	  routines to support subselects
+ *	  routines to support sub-selects appearing in expressions
 *
 * This module is concerned with executing SubPlan expression nodes, which
 * should not be confused with sub-SELECTs appearing in FROM.  SubPlans are
 * divided into "initplans", which are those that need only one evaluation per
 * query (among other restrictions, this requires that they don't use any
 * direct correlation variables from the parent plan level), and "regular"
 * subplans, which are re-evaluated every time their result is required.
 *
 *
 * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
@ -54,6 +62,8 @@ static bool slotNoNulls(TupleTableSlot *slot);
 /* ----------------------------------------------------------------
 *		ExecSubPlan
 *
 * This is the main entry point for execution of a regular SubPlan.
 * ----------------------------------------------------------------
 */
 static Datum
@ -72,7 +82,7 @@ ExecSubPlan(SubPlanState *node,
 	/* Sanity checks */
 	if (subplan->subLinkType == CTE_SUBLINK)
 		elog(ERROR, "CTE subplans should not be executed via ExecSubPlan");
-	if (subplan->setParam != NIL)
+	if (subplan->setParam != NIL && subplan->subLinkType != MULTIEXPR_SUBLINK)
 		elog(ERROR, "cannot set parent params from subquery");
 	/* Select appropriate evaluation strategy */
@ -223,6 +233,32 @@ ExecScanSubPlan(SubPlanState *node,
 	ListCell   *l;
 	ArrayBuildState *astate = NULL;
 	/*
 	 * MULTIEXPR subplans, when "executed", just return NULL; but first we
 	 * mark the subplan's output parameters as needing recalculation.  (This
 	 * is a bit of a hack: it relies on the subplan appearing later in its
 	 * targetlist than any of the referencing Params, so that all the Params
 	 * have been evaluated before we re-mark them for the next evaluation
 	 * cycle.  But in general resjunk tlist items appear after non-resjunk
 	 * ones, so this should be safe.)  Unlike ExecReScanSetParamPlan, we do
 	 * *not* set bits in the parent plan node's chgParam, because we don't
 	 * want to cause a rescan of the parent.
 	 */
 	if (subLinkType == MULTIEXPR_SUBLINK)
 	{
 		EState	   *estate = node->parent->state;
 		foreach(l, subplan->setParam)
 		{
 			int			paramid = lfirst_int(l);
 			ParamExecData *prm = &(estate->es_param_exec_vals[paramid]);
 			prm->execPlan = node;
 		}
 		*isNull = true;
 		return (Datum) 0;
 	}
 	/*
 	 * We are probably in a short-lived expression-evaluation context. Switch
 	 * to the per-query context for manipulating the child plan's chgParam,
@ -667,6 +703,9 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 	sstate->planstate = (PlanState *) list_nth(estate->es_subplanstates,
 											   subplan->plan_id - 1);
 	/* ... and to its parent's state */
 	sstate->parent = parent;
 	/* Initialize subexpressions */
 	sstate->testexpr = ExecInitExpr((Expr *) subplan->testexpr, parent);
 	sstate->args = (List *) ExecInitExpr((Expr *) subplan->args, parent);
@ -690,15 +729,16 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 	sstate->cur_eq_funcs = NULL;
 	/*
-	 * If this plan is un-correlated or undirect correlated one and want to
+	 * If this is an initplan or MULTIEXPR subplan, it has output parameters
-	 * set params for parent plan then mark parameters as needing evaluation.
+	 * that the parent plan will use, so mark those parameters as needing
 	 * evaluation.  We don't actually run the subplan until we first need one
 	 * of its outputs.
 	 *
 	 * A CTE subplan's output parameter is never to be evaluated in the normal
 	 * way, so skip this in that case.
 	 *
-	 * Note that in the case of un-correlated subqueries we don't care about
+	 * Note that we don't set parent->chgParam here: the parent plan hasn't
-	 * setting parent->chgParam here: indices take care about it, for others -
+	 * been run yet, so no need to force it to re-run.
 	 * it doesn't matter...
 	 */
 	if (subplan->setParam != NIL && subplan->subLinkType != CTE_SUBLINK)
 	{
@ -890,7 +930,7 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 /* ----------------------------------------------------------------
 *		ExecSetParamPlan
 *
- *		Executes an InitPlan subplan and sets its output parameters.
+ *		Executes a subplan and sets its output parameters.
 *
 * This is called from ExecEvalParamExec() when the value of a PARAM_EXEC
 * parameter is requested and the param's execPlan field is set (indicating
@ -908,6 +948,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 	SubLinkType subLinkType = subplan->subLinkType;
 	MemoryContext oldcontext;
 	TupleTableSlot *slot;
 	ListCell   *pvar;
 	ListCell   *l;
 	bool		found = false;
 	ArrayBuildState *astate = NULL;
@ -923,6 +964,27 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 	 */
 	oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_query_memory);
 	/*
 	 * Set Params of this plan from parent plan correlation values. (Any
 	 * calculation we have to do is done in the parent econtext, since the
 	 * Param values don't need to have per-query lifetime.)  Currently, we
 	 * expect only MULTIEXPR_SUBLINK plans to have any correlation values.
 	 */
 	Assert(subplan->parParam == NIL || subLinkType == MULTIEXPR_SUBLINK);
 	Assert(list_length(subplan->parParam) == list_length(node->args));
 	forboth(l, subplan->parParam, pvar, node->args)
 	{
 		int			paramid = lfirst_int(l);
 		ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);
 		prm->value = ExecEvalExprSwitchContext((ExprState *) lfirst(pvar),
 											   econtext,
 											   &(prm->isnull),
 											   NULL);
 		planstate->chgParam = bms_add_member(planstate->chgParam, paramid);
 	}
 	/*
 	 * Run the plan.  (If it needs to be rescanned, the first ExecProcNode
 	 * call will take care of that.)
@ -964,6 +1026,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 		if (found &&
 			(subLinkType == EXPR_SUBLINK ||
 			 subLinkType == MULTIEXPR_SUBLINK ||
 			 subLinkType == ROWCOMPARE_SUBLINK))
 			ereport(ERROR,
 					(errcode(ERRCODE_CARDINALITY_VIOLATION),
@ -1035,6 +1098,7 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 		}
 		else
 		{
 			/* For other sublink types, set all the output params to NULL */
 			foreach(l, subplan->setParam)
 			{
 				int			paramid = lfirst_int(l);
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@ -1327,6 +1327,7 @@ _copySubLink(const SubLink *from)
 	SubLink    *newnode = makeNode(SubLink);
 	COPY_SCALAR_FIELD(subLinkType);
 	COPY_SCALAR_FIELD(subLinkId);
 	COPY_NODE_FIELD(testexpr);
 	COPY_NODE_FIELD(operName);
 	COPY_NODE_FIELD(subselect);
@ -2247,6 +2248,18 @@ _copyResTarget(const ResTarget *from)
 	return newnode;
 }
 static MultiAssignRef *
 _copyMultiAssignRef(const MultiAssignRef *from)
 {
 	MultiAssignRef *newnode = makeNode(MultiAssignRef);
 	COPY_NODE_FIELD(source);
 	COPY_SCALAR_FIELD(colno);
 	COPY_SCALAR_FIELD(ncolumns);
 	return newnode;
 }
 static TypeName *
 _copyTypeName(const TypeName *from)
 {
@ -4561,6 +4574,9 @@ copyObject(const void *from)
 		case T_ResTarget:
 			retval = _copyResTarget(from);
 			break;
 		case T_MultiAssignRef:
 			retval = _copyMultiAssignRef(from);
 			break;
 		case T_TypeCast:
 			retval = _copyTypeCast(from);
 			break;
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@ -382,6 +382,7 @@ static bool
 _equalSubLink(const SubLink *a, const SubLink *b)
 {
 	COMPARE_SCALAR_FIELD(subLinkType);
 	COMPARE_SCALAR_FIELD(subLinkId);
 	COMPARE_NODE_FIELD(testexpr);
 	COMPARE_NODE_FIELD(operName);
 	COMPARE_NODE_FIELD(subselect);
@ -2094,6 +2095,16 @@ _equalResTarget(const ResTarget *a, const ResTarget *b)
 	return true;
 }
 static bool
 _equalMultiAssignRef(const MultiAssignRef *a, const MultiAssignRef *b)
 {
 	COMPARE_NODE_FIELD(source);
 	COMPARE_SCALAR_FIELD(colno);
 	COMPARE_SCALAR_FIELD(ncolumns);
 	return true;
 }
 static bool
 _equalTypeName(const TypeName *a, const TypeName *b)
 {
@ -3029,6 +3040,9 @@ equal(const void *a, const void *b)
 		case T_ResTarget:
 			retval = _equalResTarget(a, b);
 			break;
 		case T_MultiAssignRef:
 			retval = _equalMultiAssignRef(a, b);
 			break;
 		case T_TypeCast:
 			retval = _equalTypeCast(a, b);
 			break;
--- a/src/backend/nodes/list.c
+++ b/src/backend/nodes/list.c
@ -385,7 +385,7 @@ list_truncate(List *list, int new_size)
 * Locate the n'th cell (counting from 0) of the list.  It is an assertion
 * failure if there is no such cell.
 */
-static ListCell *
+ListCell *
 list_nth_cell(const List *list, int n)
 {
 	ListCell   *match;
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@ -116,6 +116,11 @@ exprType(const Node *expr)
 							format_type_be(exprType((Node *) tent->expr)))));
 					}
 				}
 				else if (sublink->subLinkType == MULTIEXPR_SUBLINK)
 				{
 					/* MULTIEXPR is always considered to return RECORD */
 					type = RECORDOID;
 				}
 				else
 				{
 					/* for all other sublink types, result is boolean */
@ -142,6 +147,11 @@ exprType(const Node *expr)
 									format_type_be(subplan->firstColType))));
 					}
 				}
 				else if (subplan->subLinkType == MULTIEXPR_SUBLINK)
 				{
 					/* MULTIEXPR is always considered to return RECORD */
 					type = RECORDOID;
 				}
 				else
 				{
 					/* for all other subplan types, result is boolean */
@ -299,6 +309,7 @@ exprTypmod(const Node *expr)
 					return exprTypmod((Node *) tent->expr);
 					/* note we don't need to care if it's an array */
 				}
 				/* otherwise, result is RECORD or BOOLEAN, typmod is -1 */
 			}
 			break;
 		case T_SubPlan:
@ -312,11 +323,7 @@ exprTypmod(const Node *expr)
 					/* note we don't need to care if it's an array */
 					return subplan->firstColTypmod;
 				}
-				else
+				/* otherwise, result is RECORD or BOOLEAN, typmod is -1 */
 				{
 					/* for all other subplan types, result is boolean */
 					return -1;
 				}
 			}
 			break;
 		case T_AlternativeSubPlan:
@ -784,7 +791,7 @@ exprCollation(const Node *expr)
 				}
 				else
 				{
-					/* for all other sublink types, result is boolean */
+					/* otherwise, result is RECORD or BOOLEAN */
 					coll = InvalidOid;
 				}
 			}
@ -802,7 +809,7 @@ exprCollation(const Node *expr)
 				}
 				else
 				{
-					/* for all other subplan types, result is boolean */
+					/* otherwise, result is RECORD or BOOLEAN */
 					coll = InvalidOid;
 				}
 			}
@ -1017,7 +1024,7 @@ exprSetCollation(Node *expr, Oid collation)
 				}
 				else
 				{
-					/* for all other sublink types, result is boolean */
+					/* otherwise, result is RECORD or BOOLEAN */
 					Assert(!OidIsValid(collation));
 				}
 			}
@ -1420,6 +1427,9 @@ exprLocation(const Node *expr)
 			/* we need not examine the contained expression (if any) */
 			loc = ((const ResTarget *) expr)->location;
 			break;
 		case T_MultiAssignRef:
 			loc = exprLocation(((const MultiAssignRef *) expr)->source);
 			break;
 		case T_TypeCast:
 			{
 				const TypeCast *tc = (const TypeCast *) expr;
@ -3107,6 +3117,8 @@ raw_expression_tree_walker(Node *node,
 					return true;
 			}
 			break;
 		case T_MultiAssignRef:
 			return walker(((MultiAssignRef *) node)->source, context);
 		case T_TypeCast:
 			{
 				TypeCast   *tc = (TypeCast *) node;
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@ -1115,6 +1115,7 @@ _outSubLink(StringInfo str, const SubLink *node)
 	WRITE_NODE_TYPE("SUBLINK");
 	WRITE_ENUM_FIELD(subLinkType, SubLinkType);
 	WRITE_INT_FIELD(subLinkId);
 	WRITE_NODE_FIELD(testexpr);
 	WRITE_NODE_FIELD(operName);
 	WRITE_NODE_FIELD(subselect);
@ -1701,6 +1702,7 @@ _outPlannerInfo(StringInfo str, const PlannerInfo *node)
 	WRITE_INT_FIELD(join_cur_level);
 	WRITE_NODE_FIELD(init_plans);
 	WRITE_NODE_FIELD(cte_plan_ids);
 	WRITE_NODE_FIELD(multiexpr_params);
 	WRITE_NODE_FIELD(eq_classes);
 	WRITE_NODE_FIELD(canon_pathkeys);
 	WRITE_NODE_FIELD(left_join_clauses);
@ -2580,6 +2582,16 @@ _outResTarget(StringInfo str, const ResTarget *node)
 	WRITE_LOCATION_FIELD(location);
 }
 static void
 _outMultiAssignRef(StringInfo str, const MultiAssignRef *node)
 {
 	WRITE_NODE_TYPE("MULTIASSIGNREF");
 	WRITE_NODE_FIELD(source);
 	WRITE_INT_FIELD(colno);
 	WRITE_INT_FIELD(ncolumns);
 }
 static void
 _outSortBy(StringInfo str, const SortBy *node)
 {
@ -3191,6 +3203,9 @@ _outNode(StringInfo str, const void *obj)
 			case T_ResTarget:
 				_outResTarget(str, obj);
 				break;
 			case T_MultiAssignRef:
 				_outMultiAssignRef(str, obj);
 				break;
 			case T_SortBy:
 				_outSortBy(str, obj);
 				break;
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@ -744,6 +744,7 @@ _readSubLink(void)
 	READ_LOCALS(SubLink);
 	READ_ENUM_FIELD(subLinkType, SubLinkType);
 	READ_INT_FIELD(subLinkId);
 	READ_NODE_FIELD(testexpr);
 	READ_NODE_FIELD(operName);
 	READ_NODE_FIELD(subselect);
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@ -310,6 +310,7 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	root->planner_cxt = CurrentMemoryContext;
 	root->init_plans = NIL;
 	root->cte_plan_ids = NIL;
 	root->multiexpr_params = NIL;
 	root->eq_classes = NIL;
 	root->append_rel_list = NIL;
 	root->rowMarks = NIL;
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@ -157,10 +157,13 @@ static bool extract_query_dependencies_walker(Node *node,
 * 3. We adjust Vars in upper plan nodes to refer to the outputs of their
 * subplans.
 *
- * 4. We compute regproc OIDs for operators (ie, we look up the function
+ * 4. PARAM_MULTIEXPR Params are replaced by regular PARAM_EXEC Params,
 * now that we have finished planning all MULTIEXPR subplans.
 *
 * 5. We compute regproc OIDs for operators (ie, we look up the function
 * that implements each op).
 *
- * 5. We create lists of specific objects that the plan depends on.
+ * 6. We create lists of specific objects that the plan depends on.
 * This will be used by plancache.c to drive invalidation of cached plans.
 * Relation dependencies are represented by OIDs, and everything else by
 * PlanInvalItems (this distinction is motivated by the shared-inval APIs).
@ -1118,11 +1121,40 @@ fix_expr_common(PlannerInfo *root, Node *node)
 	}
 }
 /*
 * fix_param_node
 *		Do set_plan_references processing on a Param
 *
 * If it's a PARAM_MULTIEXPR, replace it with the appropriate Param from
 * root->multiexpr_params; otherwise no change is needed.
 * Just for paranoia's sake, we make a copy of the node in either case.
 */
 static Node *
 fix_param_node(PlannerInfo *root, Param *p)
 {
 	if (p->paramkind == PARAM_MULTIEXPR)
 	{
 		int			subqueryid = p->paramid >> 16;
 		int			colno = p->paramid & 0xFFFF;
 		List	   *params;
 		if (subqueryid <= 0 ||
 			subqueryid > list_length(root->multiexpr_params))
 			elog(ERROR, "unexpected PARAM_MULTIEXPR ID: %d", p->paramid);
 		params = (List *) list_nth(root->multiexpr_params, subqueryid - 1);
 		if (colno <= 0 || colno > list_length(params))
 			elog(ERROR, "unexpected PARAM_MULTIEXPR ID: %d", p->paramid);
 		return copyObject(list_nth(params, colno - 1));
 	}
 	return copyObject(p);
 }
 /*
 * fix_scan_expr
 *		Do set_plan_references processing on a scan-level expression
 *
 * This consists of incrementing all Vars' varnos by rtoffset,
 * replacing PARAM_MULTIEXPR Params, expanding PlaceHolderVars,
 * looking up operator opcode info for OpExpr and related nodes,
 * and adding OIDs from regclass Const nodes into root->glob->relationOids.
 */
@ -1134,7 +1166,9 @@ fix_scan_expr(PlannerInfo *root, Node *node, int rtoffset)
 	context.root = root;
 	context.rtoffset = rtoffset;
-	if (rtoffset != 0 || root->glob->lastPHId != 0)
+	if (rtoffset != 0 ||
 		root->multiexpr_params != NIL ||
 		root->glob->lastPHId != 0)
 	{
 		return fix_scan_expr_mutator(node, &context);
 	}
@ -1142,11 +1176,12 @@ fix_scan_expr(PlannerInfo *root, Node *node, int rtoffset)
 	{
 		/*
 		 * If rtoffset == 0, we don't need to change any Vars, and if there
-		 * are no placeholders anywhere we won't need to remove them.  Then
+		 * are no MULTIEXPR subqueries then we don't need to replace
-		 * it's OK to just scribble on the input node tree instead of copying
+		 * PARAM_MULTIEXPR Params, and if there are no placeholders anywhere
-		 * (since the only change, filling in any unset opfuncid fields, is
+		 * we won't need to remove them.  Then it's OK to just scribble on the
-		 * harmless).  This saves just enough cycles to be noticeable on
+		 * input node tree instead of copying (since the only change, filling
-		 * trivial queries.
+		 * in any unset opfuncid fields, is harmless).  This saves just enough
 		 * cycles to be noticeable on trivial queries.
 		 */
 		(void) fix_scan_expr_walker(node, &context);
 		return node;
@ -1176,6 +1211,8 @@ fix_scan_expr_mutator(Node *node, fix_scan_expr_context *context)
 			var->varnoold += context->rtoffset;
 		return (Node *) var;
 	}
 	if (IsA(node, Param))
 		return fix_param_node(context->root, (Param *) node);
 	if (IsA(node, CurrentOfExpr))
 	{
 		CurrentOfExpr *cexpr = (CurrentOfExpr *) copyObject(node);
@ -1745,6 +1782,8 @@ fix_join_expr_mutator(Node *node, fix_join_expr_context *context)
 		/* If not supplied by input plans, evaluate the contained expr */
 		return fix_join_expr_mutator((Node *) phv->phexpr, context);
 	}
 	if (IsA(node, Param))
 		return fix_param_node(context->root, (Param *) node);
 	/* Try matching more complex expressions too, if tlists have any */
 	if (context->outer_itlist->has_non_vars)
 	{
@ -1847,6 +1886,8 @@ fix_upper_expr_mutator(Node *node, fix_upper_expr_context *context)
 		/* If not supplied by input plan, evaluate the contained expr */
 		return fix_upper_expr_mutator((Node *) phv->phexpr, context);
 	}
 	if (IsA(node, Param))
 		return fix_param_node(context->root, (Param *) node);
 	/* Try matching more complex expressions too, if tlist has any */
 	if (context->subplan_itlist->has_non_vars)
 	{
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@ -55,8 +55,9 @@ typedef struct finalize_primnode_context
 static Node *build_subplan(PlannerInfo *root, Plan *plan, PlannerInfo *subroot,
 			  List *plan_params,
-			  SubLinkType subLinkType, Node *testexpr,
+			  SubLinkType subLinkType, int subLinkId,
-			  bool adjust_testexpr, bool unknownEqFalse);
+			  Node *testexpr, bool adjust_testexpr,
 			  bool unknownEqFalse);
 static List *generate_subquery_params(PlannerInfo *root, List *tlist,
 						 List **paramIds);
 static List *generate_subquery_vars(PlannerInfo *root, List *tlist,
@ -407,7 +408,7 @@ get_first_col_type(Plan *plan, Oid *coltype, int32 *coltypmod,
 /*
 * Convert a SubLink (as created by the parser) into a SubPlan.
 *
- * We are given the SubLink's contained query, type, and testexpr.  We are
+ * We are given the SubLink's contained query, type, ID, and testexpr.  We are
 * also told if this expression appears at top level of a WHERE/HAVING qual.
 *
 * Note: we assume that the testexpr has been AND/OR flattened (actually,
@ -415,14 +416,20 @@ get_first_col_type(Plan *plan, Oid *coltype, int32 *coltypmod,
 * implicit-AND form; and any SubLinks in it should already have been
 * converted to SubPlans.  The subquery is as yet untouched, however.
 *
- * The result is whatever we need to substitute in place of the SubLink
+ * The result is whatever we need to substitute in place of the SubLink node
- * node in the executable expression.  This will be either the SubPlan
+ * in the executable expression.  If we're going to do the subplan as a
- * node (if we have to do the subplan as a subplan), or a Param node
+ * regular subplan, this will be the constructed SubPlan node.  If we're going
- * representing the result of an InitPlan, or a row comparison expression
+ * to do the subplan as an InitPlan, the SubPlan node instead goes into
- * tree containing InitPlan Param nodes.
+ * root->init_plans, and what we return here is an expression tree
 * representing the InitPlan's result: usually just a Param node representing
 * a single scalar result, but possibly a row comparison tree containing
 * multiple Param nodes, or for a MULTIEXPR subquery a simple NULL constant
 * (since the real output Params are elsewhere in the tree, and the MULTIEXPR
 * subquery itself is in a resjunk tlist entry whose value is uninteresting).
 */
 static Node *
-make_subplan(PlannerInfo *root, Query *orig_subquery, SubLinkType subLinkType,
+make_subplan(PlannerInfo *root, Query *orig_subquery,
 			 SubLinkType subLinkType, int subLinkId,
 			 Node *testexpr, bool isTopQual)
 {
 	Query	   *subquery;
@ -452,8 +459,8 @@ make_subplan(PlannerInfo *root, Query *orig_subquery, SubLinkType subLinkType,
 	 * first tuple will be retrieved.  For ALL and ANY subplans, we will be
 	 * able to stop evaluating if the test condition fails or matches, so very
 	 * often not all the tuples will be retrieved; for lack of a better idea,
-	 * specify 50% retrieval.  For EXPR and ROWCOMPARE subplans, use default
+	 * specify 50% retrieval.  For EXPR, MULTIEXPR, and ROWCOMPARE subplans,
-	 * behavior (we're only expecting one row out, anyway).
+	 * use default behavior (we're only expecting one row out, anyway).
 	 *
 	 * NOTE: if you change these numbers, also change cost_subplan() in
 	 * path/costsize.c.
@ -491,7 +498,8 @@ make_subplan(PlannerInfo *root, Query *orig_subquery, SubLinkType subLinkType,
 	/* And convert to SubPlan or InitPlan format. */
 	result = build_subplan(root, plan, subroot, plan_params,
-						   subLinkType, testexpr, true, isTopQual);
+						   subLinkType, subLinkId,
 						   testexpr, true, isTopQual);
 	/*
 	 * If it's a correlated EXISTS with an unimportant targetlist, we might be
@ -536,7 +544,8 @@ make_subplan(PlannerInfo *root, Query *orig_subquery, SubLinkType subLinkType,
 				/* OK, convert to SubPlan format. */
 				hashplan = (SubPlan *) build_subplan(root, plan, subroot,
 													 plan_params,
-													 ANY_SUBLINK, newtestexpr,
+													 ANY_SUBLINK, 0,
 													 newtestexpr,
 													 false, true);
 				/* Check we got what we expected */
 				Assert(IsA(hashplan, SubPlan));
@ -559,14 +568,15 @@ make_subplan(PlannerInfo *root, Query *orig_subquery, SubLinkType subLinkType,
 /*
 * Build a SubPlan node given the raw inputs --- subroutine for make_subplan
 *
- * Returns either the SubPlan, or an expression using initplan output Params,
+ * Returns either the SubPlan, or a replacement expression if we decide to
- * as explained in the comments for make_subplan.
+ * make it an InitPlan, as explained in the comments for make_subplan.
 */
 static Node *
 build_subplan(PlannerInfo *root, Plan *plan, PlannerInfo *subroot,
 			  List *plan_params,
-			  SubLinkType subLinkType, Node *testexpr,
+			  SubLinkType subLinkType, int subLinkId,
-			  bool adjust_testexpr, bool unknownEqFalse)
+			  Node *testexpr, bool adjust_testexpr,
 			  bool unknownEqFalse)
 {
 	Node	   *result;
 	SubPlan    *splan;
@ -615,12 +625,15 @@ build_subplan(PlannerInfo *root, Plan *plan, PlannerInfo *subroot,
 	}
 	/*
-	 * Un-correlated or undirect correlated plans of EXISTS, EXPR, ARRAY, or
+	 * Un-correlated or undirect correlated plans of EXISTS, EXPR, ARRAY,
-	 * ROWCOMPARE types can be used as initPlans.  For EXISTS, EXPR, or ARRAY,
+	 * ROWCOMPARE, or MULTIEXPR types can be used as initPlans.  For EXISTS,
-	 * we just produce a Param referring to the result of evaluating the
+	 * EXPR, or ARRAY, we return a Param referring to the result of evaluating
-	 * initPlan.  For ROWCOMPARE, we must modify the testexpr tree to contain
+	 * the initPlan.  For ROWCOMPARE, we must modify the testexpr tree to
-	 * PARAM_EXEC Params instead of the PARAM_SUBLINK Params emitted by the
+	 * contain PARAM_EXEC Params instead of the PARAM_SUBLINK Params emitted
-	 * parser.
+	 * by the parser, and then return that tree.  For MULTIEXPR, we return a
 	 * null constant: the resjunk targetlist item containing the SubLink does
 	 * not need to return anything useful, since the referencing Params are
 	 * elsewhere.
 	 */
 	if (splan->parParam == NIL && subLinkType == EXISTS_SUBLINK)
 	{
@ -687,6 +700,42 @@ build_subplan(PlannerInfo *root, Plan *plan, PlannerInfo *subroot,
 		 * plan's expression tree; it is not kept in the initplan node.
 		 */
 	}
 	else if (subLinkType == MULTIEXPR_SUBLINK)
 	{
 		/*
 		 * Whether it's an initplan or not, it needs to set a PARAM_EXEC Param
 		 * for each output column.
 		 */
 		List	   *params;
 		Assert(testexpr == NULL);
 		params = generate_subquery_params(root,
 										  plan->targetlist,
 										  &splan->setParam);
 		/*
 		 * Save the list of replacement Params in the n'th cell of
 		 * root->multiexpr_params; setrefs.c will use it to replace
 		 * PARAM_MULTIEXPR Params.
 		 */
 		while (list_length(root->multiexpr_params) < subLinkId)
 			root->multiexpr_params = lappend(root->multiexpr_params, NIL);
 		lc = list_nth_cell(root->multiexpr_params, subLinkId - 1);
 		Assert(lfirst(lc) == NIL);
 		lfirst(lc) = params;
 		/* It can be an initplan if there are no parParams. */
 		if (splan->parParam == NIL)
 		{
 			isInitPlan = true;
 			result = (Node *) makeNullConst(RECORDOID, -1, InvalidOid);
 		}
 		else
 		{
 			isInitPlan = false;
 			result = (Node *) splan;
 		}
 	}
 	else
 	{
 		/*
@ -760,25 +809,22 @@ build_subplan(PlannerInfo *root, Plan *plan, PlannerInfo *subroot,
 												   splan->plan_id);
 	/* Label the subplan for EXPLAIN purposes */
-	if (isInitPlan)
+	splan->plan_name = palloc(32 + 12 * list_length(splan->setParam));
 	sprintf(splan->plan_name, "%s %d",
 			isInitPlan ? "InitPlan" : "SubPlan",
 			splan->plan_id);
 	if (splan->setParam)
 	{
-		ListCell   *lc;
+		char	   *ptr = splan->plan_name + strlen(splan->plan_name);
 		int			offset;
-		splan->plan_name = palloc(32 + 12 * list_length(splan->setParam));
+		ptr += sprintf(ptr, " (returns ");
 		sprintf(splan->plan_name, "InitPlan %d (returns ", splan->plan_id);
 		offset = strlen(splan->plan_name);
 		foreach(lc, splan->setParam)
 		{
-			sprintf(splan->plan_name + offset, "$%d%s",
+			ptr += sprintf(ptr, "$%d%s",
-					lfirst_int(lc),
+						   lfirst_int(lc),
-					lnext(lc) ? "," : "");
+						   lnext(lc) ? "," : ")");
 			offset += strlen(splan->plan_name + offset);
 		}
 		sprintf(splan->plan_name + offset, ")");
 	}
 	else
 		splan->plan_name = psprintf("SubPlan %d", splan->plan_id);
 	/* Lastly, fill in the cost estimates for use later */
 	cost_subplan(root, splan, plan);
@ -1816,6 +1862,7 @@ process_sublinks_mutator(Node *node, process_sublinks_context *context)
 		return make_subplan(context->root,
 							(Query *) sublink->subselect,
 							sublink->subLinkType,
 							sublink->subLinkId,
 							testexpr,
 							context->isTopQual);
 	}
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@ -804,6 +804,7 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	subroot->planner_cxt = CurrentMemoryContext;
 	subroot->init_plans = NIL;
 	subroot->cte_plan_ids = NIL;
 	subroot->multiexpr_params = NIL;
 	subroot->eq_classes = NIL;
 	subroot->append_rel_list = NIL;
 	subroot->rowMarks = NIL;
--- a/src/backend/optimizer/util/tlist.c
+++ b/src/backend/optimizer/util/tlist.c
@ -187,6 +187,27 @@ get_tlist_exprs(List *tlist, bool includeJunk)
 }
 /*
 * count_nonjunk_tlist_entries
 *		What it says ...
 */
 int
 count_nonjunk_tlist_entries(List *tlist)
 {
 	int			len = 0;
 	ListCell   *l;
 	foreach(l, tlist)
 	{
 		TargetEntry *tle = (TargetEntry *) lfirst(l);
 		if (!tle->resjunk)
 			len++;
 	}
 	return len;
 }
 /*
 * tlist_same_exprs
 *		Check whether two target lists contain the same expressions
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@ -9234,6 +9234,14 @@ single_set_clause:
 				}
 		;
 /*
 * Ideally, we'd accept any row-valued a_expr as RHS of a multiple_set_clause.
 * However, per SQL spec the row-constructor case must allow DEFAULT as a row
 * member, and it's pretty unclear how to do that (unless perhaps we allow
 * DEFAULT in any a_expr and let parse analysis sort it out later?).  For the
 * moment, the planner/executor only support a subquery as a multiassignment
 * source anyhow, so we need only accept ctext_row and subqueries here.
 */
 multiple_set_clause:
 			'(' set_target_list ')' '=' ctext_row
 				{
@ -9242,14 +9250,15 @@ multiple_set_clause:
 					/*
 					 * Break the ctext_row apart, merge individual expressions
-					 * into the destination ResTargets.  XXX this approach
+					 * into the destination ResTargets.  This is semantically
-					 * cannot work for general row expressions as sources.
+					 * equivalent to, and much cheaper to process than, the
 					 * general case.
 					 */
 					if (list_length($2) != list_length($5))
 						ereport(ERROR,
 								(errcode(ERRCODE_SYNTAX_ERROR),
 								 errmsg("number of columns does not match number of values"),
-								 parser_errposition(@1)));
+								 parser_errposition(@5)));
 					forboth(col_cell, $2, val_cell, $5)
 					{
 						ResTarget *res_col = (ResTarget *) lfirst(col_cell);
@ -9258,6 +9267,36 @@ multiple_set_clause:
 						res_col->val = res_val;
 					}
 					$$ = $2;
 				}
 			| '(' set_target_list ')' '=' select_with_parens
 				{
 					SubLink *sl = makeNode(SubLink);
 					int ncolumns = list_length($2);
 					int i = 1;
 					ListCell *col_cell;
 					/* First, convert bare SelectStmt into a SubLink */
 					sl->subLinkType = MULTIEXPR_SUBLINK;
 					sl->subLinkId = 0;		/* will be assigned later */
 					sl->testexpr = NULL;
 					sl->operName = NIL;
 					sl->subselect = $5;
 					sl->location = @5;
 					/* Create a MultiAssignRef source for each target */
 					foreach(col_cell, $2)
 					{
 						ResTarget *res_col = (ResTarget *) lfirst(col_cell);
 						MultiAssignRef *r = makeNode(MultiAssignRef);
 						r->source = (Node *) sl;
 						r->colno = i;
 						r->ncolumns = ncolumns;
 						res_col->val = (Node *) r;
 						i++;
 					}
 					$$ = $2;
 				}
 		;
@ -11091,6 +11130,7 @@ a_expr:		c_expr									{ $$ = $1; }
 						/* generate foo = ANY (subquery) */
 						SubLink *n = (SubLink *) $3;
 						n->subLinkType = ANY_SUBLINK;
 						n->subLinkId = 0;
 						n->testexpr = $1;
 						n->operName = list_make1(makeString("="));
 						n->location = @2;
@ -11111,6 +11151,7 @@ a_expr:		c_expr									{ $$ = $1; }
 						/* Make an = ANY node */
 						SubLink *n = (SubLink *) $4;
 						n->subLinkType = ANY_SUBLINK;
 						n->subLinkId = 0;
 						n->testexpr = $1;
 						n->operName = list_make1(makeString("="));
 						n->location = @3;
@ -11127,6 +11168,7 @@ a_expr:		c_expr									{ $$ = $1; }
 				{
 					SubLink *n = makeNode(SubLink);
 					n->subLinkType = $3;
 					n->subLinkId = 0;
 					n->testexpr = $1;
 					n->operName = $2;
 					n->subselect = $4;
@ -11286,6 +11328,7 @@ c_expr:		columnref								{ $$ = $1; }
 				{
 					SubLink *n = makeNode(SubLink);
 					n->subLinkType = EXPR_SUBLINK;
 					n->subLinkId = 0;
 					n->testexpr = NULL;
 					n->operName = NIL;
 					n->subselect = $1;
@ -11307,6 +11350,7 @@ c_expr:		columnref								{ $$ = $1; }
 					SubLink *n = makeNode(SubLink);
 					A_Indirection *a = makeNode(A_Indirection);
 					n->subLinkType = EXPR_SUBLINK;
 					n->subLinkId = 0;
 					n->testexpr = NULL;
 					n->operName = NIL;
 					n->subselect = $1;
@ -11319,6 +11363,7 @@ c_expr:		columnref								{ $$ = $1; }
 				{
 					SubLink *n = makeNode(SubLink);
 					n->subLinkType = EXISTS_SUBLINK;
 					n->subLinkId = 0;
 					n->testexpr = NULL;
 					n->operName = NIL;
 					n->subselect = $2;
@ -11329,6 +11374,7 @@ c_expr:		columnref								{ $$ = $1; }
 				{
 					SubLink *n = makeNode(SubLink);
 					n->subLinkType = ARRAY_SUBLINK;
 					n->subLinkId = 0;
 					n->testexpr = NULL;
 					n->operName = NIL;
 					n->subselect = $2;
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@ -20,6 +20,7 @@
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/tlist.h"
 #include "optimizer/var.h"
 #include "parser/analyze.h"
 #include "parser/parse_clause.h"
@ -49,6 +50,7 @@ static Node *transformAExprOf(ParseState *pstate, A_Expr *a);
 static Node *transformAExprIn(ParseState *pstate, A_Expr *a);
 static Node *transformBoolExpr(ParseState *pstate, BoolExpr *a);
 static Node *transformFuncCall(ParseState *pstate, FuncCall *fn);
 static Node *transformMultiAssignRef(ParseState *pstate, MultiAssignRef *maref);
 static Node *transformCaseExpr(ParseState *pstate, CaseExpr *c);
 static Node *transformSubLink(ParseState *pstate, SubLink *sublink);
 static Node *transformArrayExpr(ParseState *pstate, A_ArrayExpr *a,
@ -255,6 +257,10 @@ transformExprRecurse(ParseState *pstate, Node *expr)
 			result = transformFuncCall(pstate, (FuncCall *) expr);
 			break;
 		case T_MultiAssignRef:
 			result = transformMultiAssignRef(pstate, (MultiAssignRef *) expr);
 			break;
 		case T_NamedArgExpr:
 			{
 				NamedArgExpr *na = (NamedArgExpr *) expr;
@ -1267,6 +1273,80 @@ transformFuncCall(ParseState *pstate, FuncCall *fn)
 							 fn->location);
 }
 static Node *
 transformMultiAssignRef(ParseState *pstate, MultiAssignRef *maref)
 {
 	SubLink    *sublink;
 	Query	   *qtree;
 	TargetEntry *tle;
 	Param	   *param;
 	/* We should only see this in first-stage processing of UPDATE tlists */
 	Assert(pstate->p_expr_kind == EXPR_KIND_UPDATE_SOURCE);
 	/* We only need to transform the source if this is the first column */
 	if (maref->colno == 1)
 	{
 		sublink = (SubLink *) transformExprRecurse(pstate, maref->source);
 		/* Currently, the grammar only allows a SubLink as source */
 		Assert(IsA(sublink, SubLink));
 		Assert(sublink->subLinkType == MULTIEXPR_SUBLINK);
 		qtree = (Query *) sublink->subselect;
 		Assert(IsA(qtree, Query));
 		/* Check subquery returns required number of columns */
 		if (count_nonjunk_tlist_entries(qtree->targetList) != maref->ncolumns)
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("number of columns does not match number of values"),
 					 parser_errposition(pstate, sublink->location)));
 		/*
 		 * Build a resjunk tlist item containing the MULTIEXPR SubLink, and
 		 * add it to pstate->p_multiassign_exprs, whence it will later get
 		 * appended to the completed targetlist.  We needn't worry about
 		 * selecting a resno for it; transformUpdateStmt will do that.
 		 */
 		tle = makeTargetEntry((Expr *) sublink, 0, NULL, true);
 		pstate->p_multiassign_exprs = lappend(pstate->p_multiassign_exprs, tle);
 		/*
 		 * Assign a unique-within-this-targetlist ID to the MULTIEXPR SubLink.
 		 * We can just use its position in the p_multiassign_exprs list.
 		 */
 		sublink->subLinkId = list_length(pstate->p_multiassign_exprs);
 	}
 	else
 	{
 		/*
 		 * Second or later column in a multiassignment.  Re-fetch the
 		 * transformed query, which we assume is still the last entry in
 		 * p_multiassign_exprs.
 		 */
 		Assert(pstate->p_multiassign_exprs != NIL);
 		tle = (TargetEntry *) llast(pstate->p_multiassign_exprs);
 		sublink = (SubLink *) tle->expr;
 		Assert(IsA(sublink, SubLink));
 		Assert(sublink->subLinkType == MULTIEXPR_SUBLINK);
 		qtree = (Query *) sublink->subselect;
 		Assert(IsA(qtree, Query));
 	}
 	/* Build a Param representing the appropriate subquery output column */
 	tle = (TargetEntry *) list_nth(qtree->targetList, maref->colno - 1);
 	Assert(!tle->resjunk);
 	param = makeNode(Param);
 	param->paramkind = PARAM_MULTIEXPR;
 	param->paramid = (sublink->subLinkId << 16) | maref->colno;
 	param->paramtype = exprType((Node *) tle->expr);
 	param->paramtypmod = exprTypmod((Node *) tle->expr);
 	param->paramcollid = exprCollation((Node *) tle->expr);
 	param->location = exprLocation((Node *) tle->expr);
 	return (Node *) param;
 }
 static Node *
 transformCaseExpr(ParseState *pstate, CaseExpr *c)
 {
@ -1520,26 +1600,15 @@ transformSubLink(ParseState *pstate, SubLink *sublink)
 	else if (sublink->subLinkType == EXPR_SUBLINK ||
 			 sublink->subLinkType == ARRAY_SUBLINK)
 	{
 		ListCell   *tlist_item = list_head(qtree->targetList);
 		/*
 		 * Make sure the subselect delivers a single column (ignoring resjunk
 		 * targets).
 		 */
-		if (tlist_item == NULL ||
+		if (count_nonjunk_tlist_entries(qtree->targetList) != 1)
 			((TargetEntry *) lfirst(tlist_item))->resjunk)
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
-					 errmsg("subquery must return a column"),
+					 errmsg("subquery must return only one column"),
 					 parser_errposition(pstate, sublink->location)));
 		while ((tlist_item = lnext(tlist_item)) != NULL)
 		{
 			if (!((TargetEntry *) lfirst(tlist_item))->resjunk)
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("subquery must return only one column"),
 						 parser_errposition(pstate, sublink->location)));
 		}
 		/*
 		 * EXPR and ARRAY need no test expression or combining operator. These
@ -1548,6 +1617,12 @@ transformSubLink(ParseState *pstate, SubLink *sublink)
 		sublink->testexpr = NULL;
 		sublink->operName = NIL;
 	}
 	else if (sublink->subLinkType == MULTIEXPR_SUBLINK)
 	{
 		/* Same as EXPR case, except no restriction on number of columns */
 		sublink->testexpr = NULL;
 		sublink->operName = NIL;
 	}
 	else
 	{
 		/* ALL, ANY, or ROWCOMPARE: generate row-comparing expression */
--- a/src/backend/parser/parse_target.c
+++ b/src/backend/parser/parse_target.c
@ -113,9 +113,9 @@ transformTargetEntry(ParseState *pstate,
 * transformTargetList()
 * Turns a list of ResTarget's into a list of TargetEntry's.
 *
- * At this point, we don't care whether we are doing SELECT, UPDATE,
+ * This code acts mostly the same for SELECT, UPDATE, or RETURNING lists;
- * or RETURNING; we just transform the given expressions (the "val" fields).
+ * the main thing is to transform the given expressions (the "val" fields).
- * However, our subroutines care, so we need the exprKind parameter.
+ * The exprKind parameter distinguishes these cases when necesssary.
 */
 List *
 transformTargetList(ParseState *pstate, List *targetlist,
@ -124,6 +124,9 @@ transformTargetList(ParseState *pstate, List *targetlist,
 	List	   *p_target = NIL;
 	ListCell   *o_target;
 	/* Shouldn't have any leftover multiassign items at start */
 	Assert(pstate->p_multiassign_exprs == NIL);
 	foreach(o_target, targetlist)
 	{
 		ResTarget  *res = (ResTarget *) lfirst(o_target);
@ -172,6 +175,19 @@ transformTargetList(ParseState *pstate, List *targetlist,
 												false));
 	}
 	/*
 	 * If any multiassign resjunk items were created, attach them to the end
 	 * of the targetlist.  This should only happen in an UPDATE tlist.  We
 	 * don't need to worry about numbering of these items; transformUpdateStmt
 	 * will set their resnos.
 	 */
 	if (pstate->p_multiassign_exprs)
 	{
 		Assert(exprKind == EXPR_KIND_UPDATE_SOURCE);
 		p_target = list_concat(p_target, pstate->p_multiassign_exprs);
 		pstate->p_multiassign_exprs = NIL;
 	}
 	return p_target;
 }
@ -234,6 +250,9 @@ transformExpressionList(ParseState *pstate, List *exprlist,
 						 transformExpr(pstate, e, exprKind));
 	}
 	/* Shouldn't have any multiassign items here */
 	Assert(pstate->p_multiassign_exprs == NIL);
 	return result;
 }
@ -1691,6 +1710,7 @@ FigureColnameInternal(Node *node, char **name)
 					}
 					break;
 					/* As with other operator-like nodes, these have no names */
 				case MULTIEXPR_SUBLINK:
 				case ALL_SUBLINK:
 				case ANY_SUBLINK:
 				case ROWCOMPARE_SUBLINK:
--- a/src/backend/rewrite/rewriteManip.c
+++ b/src/backend/rewrite/rewriteManip.c
@ -281,6 +281,26 @@ checkExprHasSubLink_walker(Node *node, void *context)
 	return expression_tree_walker(node, checkExprHasSubLink_walker, context);
 }
 /*
 * Check for MULTIEXPR Param within expression tree
 *
 * We intentionally don't descend into SubLinks: only Params at the current
 * query level are of interest.
 */
 static bool
 contains_multiexpr_param(Node *node, void *context)
 {
 	if (node == NULL)
 		return false;
 	if (IsA(node, Param))
 	{
 		if (((Param *) node)->paramkind == PARAM_MULTIEXPR)
 			return true;		/* abort the tree traversal and return true */
 		return false;
 	}
 	return expression_tree_walker(node, contains_multiexpr_param, context);
 }
 /*
 * OffsetVarNodes - adjust Vars when appending one query's RT to another
@ -1370,6 +1390,21 @@ ReplaceVarsFromTargetList_callback(Var *var,
 		if (var->varlevelsup > 0)
 			IncrementVarSublevelsUp(newnode, var->varlevelsup, 0);
 		/*
 		 * Check to see if the tlist item contains a PARAM_MULTIEXPR Param,
 		 * and throw error if so.  This case could only happen when expanding
 		 * an ON UPDATE rule's NEW variable and the referenced tlist item in
 		 * the original UPDATE command is part of a multiple assignment. There
 		 * seems no practical way to handle such cases without multiple
 		 * evaluation of the multiple assignment's sub-select, which would
 		 * create semantic oddities that users of rules would probably prefer
 		 * not to cope with.  So treat it as an unimplemented feature.
 		 */
 		if (contains_multiexpr_param(newnode, NULL))
 			ereport(ERROR,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					 errmsg("NEW variables in ON UPDATE rules cannot reference columns that are part of a multiple assignment in the subject UPDATE command")));
 		return newnode;
 	}
 }
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@ -5228,8 +5228,12 @@ static void
 get_update_query_def(Query *query, deparse_context *context)
 {
 	StringInfo	buf = context->buf;
 	char	   *sep;
 	RangeTblEntry *rte;
 	List	   *ma_sublinks;
 	ListCell   *next_ma_cell;
 	SubLink    *cur_ma_sublink;
 	int			remaining_ma_columns;
 	const char *sep;
 	ListCell   *l;
 	/* Insert the WITH clause if given */
@ -5253,6 +5257,34 @@ get_update_query_def(Query *query, deparse_context *context)
 						 quote_identifier(rte->alias->aliasname));
 	appendStringInfoString(buf, " SET ");
 	/*
 	 * Prepare to deal with MULTIEXPR assignments: collect the source SubLinks
 	 * into a list.  We expect them to appear, in ID order, in resjunk tlist
 	 * entries.
 	 */
 	ma_sublinks = NIL;
 	if (query->hasSubLinks)		/* else there can't be any */
 	{
 		foreach(l, query->targetList)
 		{
 			TargetEntry *tle = (TargetEntry *) lfirst(l);
 			if (tle->resjunk && IsA(tle->expr, SubLink))
 			{
 				SubLink    *sl = (SubLink *) tle->expr;
 				if (sl->subLinkType == MULTIEXPR_SUBLINK)
 				{
 					ma_sublinks = lappend(ma_sublinks, sl);
 					Assert(sl->subLinkId == list_length(ma_sublinks));
 				}
 			}
 		}
 	}
 	next_ma_cell = list_head(ma_sublinks);
 	cur_ma_sublink = NULL;
 	remaining_ma_columns = 0;
 	/* Add the comma separated list of 'attname = value' */
 	sep = "";
 	foreach(l, query->targetList)
@ -5263,9 +5295,57 @@ get_update_query_def(Query *query, deparse_context *context)
 		if (tle->resjunk)
 			continue;			/* ignore junk entries */
 		/* Emit separator (OK whether we're in multiassignment or not) */
 		appendStringInfoString(buf, sep);
 		sep = ", ";
 		/*
 		 * Check to see if we're starting a multiassignment group: if so,
 		 * output a left paren.
 		 */
 		if (next_ma_cell != NULL && cur_ma_sublink == NULL)
 		{
 			/*
 			 * We must dig down into the expr to see if it's a PARAM_MULTIEXPR
 			 * Param.  That could be buried under FieldStores and ArrayRefs
 			 * (cf processIndirection()), and underneath those there could be
 			 * an implicit type coercion.
 			 */
 			expr = (Node *) tle->expr;
 			while (expr)
 			{
 				if (IsA(expr, FieldStore))
 				{
 					FieldStore *fstore = (FieldStore *) expr;
 					expr = (Node *) linitial(fstore->newvals);
 				}
 				else if (IsA(expr, ArrayRef))
 				{
 					ArrayRef   *aref = (ArrayRef *) expr;
 					if (aref->refassgnexpr == NULL)
 						break;
 					expr = (Node *) aref->refassgnexpr;
 				}
 				else
 					break;
 			}
 			expr = strip_implicit_coercions(expr);
 			if (expr && IsA(expr, Param) &&
 				((Param *) expr)->paramkind == PARAM_MULTIEXPR)
 			{
 				cur_ma_sublink = (SubLink *) lfirst(next_ma_cell);
 				next_ma_cell = lnext(next_ma_cell);
 				remaining_ma_columns = count_nonjunk_tlist_entries(
 						  ((Query *) cur_ma_sublink->subselect)->targetList);
 				Assert(((Param *) expr)->paramid ==
 					   ((cur_ma_sublink->subLinkId << 16) | 1));
 				appendStringInfoChar(buf, '(');
 			}
 		}
 		/*
 		 * Put out name of target column; look in the catalogs, not at
 		 * tle->resname, since resname will fail to track RENAME.
@ -5280,6 +5360,20 @@ get_update_query_def(Query *query, deparse_context *context)
 		 */
 		expr = processIndirection((Node *) tle->expr, context, true);
 		/*
 		 * If we're in a multiassignment, skip printing anything more, unless
 		 * this is the last column; in which case, what we print should be the
 		 * sublink, not the Param.
 		 */
 		if (cur_ma_sublink != NULL)
 		{
 			if (--remaining_ma_columns > 0)
 				continue;		/* not the last column of multiassignment */
 			appendStringInfoChar(buf, ')');
 			expr = (Node *) cur_ma_sublink;
 			cur_ma_sublink = NULL;
 		}
 		appendStringInfoString(buf, " = ");
 		get_rule_expr(expr, context, false);
@ -8123,6 +8217,7 @@ get_sublink_expr(SubLink *sublink, deparse_context *context)
 			break;
 		case EXPR_SUBLINK:
 		case MULTIEXPR_SUBLINK:
 		case ARRAY_SUBLINK:
 			need_paren = false;
 			break;
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@ -53,6 +53,6 @@
 */
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201406121
+#define CATALOG_VERSION_NO	201406181
 #endif
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@ -728,6 +728,7 @@ typedef struct SubPlanState
 {
 	ExprState	xprstate;
 	struct PlanState *planstate;	/* subselect plan's state tree */
 	struct PlanState *parent;	/* parent plan node's state tree */
 	ExprState  *testexpr;		/* state of combining expression */
 	List	   *args;			/* states of argument expression(s) */
 	HeapTuple	curTuple;		/* copy of most recent tuple from subplan */
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@ -379,6 +379,7 @@ typedef enum NodeTag
 	T_A_Indirection,
 	T_A_ArrayExpr,
 	T_ResTarget,
 	T_MultiAssignRef,
 	T_TypeCast,
 	T_CollateClause,
 	T_SortBy,
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@ -384,6 +384,23 @@ typedef struct ResTarget
 	int			location;		/* token location, or -1 if unknown */
 } ResTarget;
 /*
 * MultiAssignRef - element of a row source expression for UPDATE
 *
 * In an UPDATE target list, when we have SET (a,b,c) = row-valued-expression,
 * we generate separate ResTarget items for each of a,b,c.  Their "val" trees
 * are MultiAssignRef nodes numbered 1..n, linking to a common copy of the
 * row-valued-expression (which parse analysis will process only once, when
 * handling the MultiAssignRef with colno=1).
 */
 typedef struct MultiAssignRef
 {
 	NodeTag		type;
 	Node	   *source;			/* the row-valued expression */
 	int			colno;			/* column number for this target (1..n) */
 	int			ncolumns;		/* number of targets in the construct */
 } MultiAssignRef;
 /*
 * SortBy - for ORDER BY clause
 */
--- a/src/include/nodes/pg_list.h
+++ b/src/include/nodes/pg_list.h
@ -206,6 +206,7 @@ extern List *lcons_oid(Oid datum, List *list);
 extern List *list_concat(List *list1, List *list2);
 extern List *list_truncate(List *list, int new_size);
 extern ListCell *list_nth_cell(const List *list, int n);
 extern void *list_nth(const List *list, int n);
 extern int	list_nth_int(const List *list, int n);
 extern Oid	list_nth_oid(const List *list, int n);
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@ -198,17 +198,25 @@ typedef struct Const
 *				`paramid' field.  (This type of Param is converted to
 *				PARAM_EXEC during planning.)
 *
- * Note: currently, paramtypmod is valid for PARAM_SUBLINK Params, and for
+ *		PARAM_MULTIEXPR:  Like PARAM_SUBLINK, the parameter represents an
- * PARAM_EXEC Params generated from them; it is always -1 for PARAM_EXTERN
+ *				output column of a SubLink node's sub-select, but here, the
- * params, since the APIs that supply values for such parameters don't carry
+ *				SubLink is always a MULTIEXPR SubLink.  The high-order 16 bits
- * any typmod info.
+ *				of the `paramid' field contain the SubLink's subLinkId, and
 *				the low-order 16 bits contain the column number.  (This type
 *				of Param is also converted to PARAM_EXEC during planning.)
 *
 * Note: currently, paramtypmod is always -1 for PARAM_EXTERN params, since
 * the APIs that supply values for such parameters don't carry any typmod
 * info.  It is valid in other types of Params, if they represent expressions
 * with determinable typmod.
 * ----------------
 */
 typedef enum ParamKind
 {
 	PARAM_EXTERN,
 	PARAM_EXEC,
-	PARAM_SUBLINK
+	PARAM_SUBLINK,
 	PARAM_MULTIEXPR
 } ParamKind;
 typedef struct Param
@ -485,14 +493,16 @@ typedef struct BoolExpr
 *	ANY_SUBLINK			(lefthand) op ANY (SELECT ...)
 *	ROWCOMPARE_SUBLINK	(lefthand) op (SELECT ...)
 *	EXPR_SUBLINK		(SELECT with single targetlist item ...)
 *	MULTIEXPR_SUBLINK	(SELECT with multiple targetlist items ...)
 *	ARRAY_SUBLINK		ARRAY(SELECT with single targetlist item ...)
 *	CTE_SUBLINK			WITH query (never actually part of an expression)
 * For ALL, ANY, and ROWCOMPARE, the lefthand is a list of expressions of the
 * same length as the subselect's targetlist.  ROWCOMPARE will *always* have
 * a list with more than one entry; if the subselect has just one target
 * then the parser will create an EXPR_SUBLINK instead (and any operator
- * above the subselect will be represented separately).  Note that both
+ * above the subselect will be represented separately).
- * ROWCOMPARE and EXPR require the subselect to deliver only one row.
+ * ROWCOMPARE, EXPR, and MULTIEXPR require the subselect to deliver at most
 * one row (if it returns no rows, the result is NULL).
 * ALL, ANY, and ROWCOMPARE require the combining operators to deliver boolean
 * results.  ALL and ANY combine the per-row results using AND and OR
 * semantics respectively.
@ -511,8 +521,14 @@ typedef struct BoolExpr
 * output columns of the subselect.  And subselect is transformed to a Query.
 * This is the representation seen in saved rules and in the rewriter.
 *
- * In EXISTS, EXPR, and ARRAY SubLinks, testexpr and operName are unused and
+ * In EXISTS, EXPR, MULTIEXPR, and ARRAY SubLinks, testexpr and operName
- * are always null.
+ * are unused and are always null.
 *
 * subLinkId is currently used only for MULTIEXPR SubLinks, and is zero in
 * other SubLinks.  This number identifies different multiple-assignment
 * subqueries within an UPDATE statement's SET list.  It is unique only
 * within a particular targetlist.  The output column(s) of the MULTIEXPR
 * are referenced by PARAM_MULTIEXPR Params appearing elsewhere in the tlist.
 *
 * The CTE_SUBLINK case never occurs in actual SubLink nodes, but it is used
 * in SubPlans generated for WITH subqueries.
@ -524,6 +540,7 @@ typedef enum SubLinkType
 	ANY_SUBLINK,
 	ROWCOMPARE_SUBLINK,
 	EXPR_SUBLINK,
 	MULTIEXPR_SUBLINK,
 	ARRAY_SUBLINK,
 	CTE_SUBLINK					/* for SubPlans only */
 } SubLinkType;
@ -533,9 +550,10 @@ typedef struct SubLink
 {
 	Expr		xpr;
 	SubLinkType subLinkType;	/* see above */
 	int			subLinkId;		/* ID (1..n); 0 if not MULTIEXPR */
 	Node	   *testexpr;		/* outer-query test for ALL/ANY/ROWCOMPARE */
 	List	   *operName;		/* originally specified operator name */
-	Node	   *subselect;		/* subselect as Query* or parsetree */
+	Node	   *subselect;		/* subselect as Query* or raw parsetree */
 	int			location;		/* token location, or -1 if unknown */
 } SubLink;
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@ -190,6 +190,9 @@ typedef struct PlannerInfo
 	List	   *cte_plan_ids;	/* per-CTE-item list of subplan IDs */
 	List	   *multiexpr_params;		/* List of Lists of Params for
 										 * MULTIEXPR subquery outputs */
 	List	   *eq_classes;		/* list of active EquivalenceClasses */
 	List	   *canon_pathkeys; /* list of "canonical" PathKeys */
--- a/src/include/optimizer/tlist.h
+++ b/src/include/optimizer/tlist.h
@ -27,6 +27,8 @@ extern List *add_to_flat_tlist(List *tlist, List *exprs);
 extern List *get_tlist_exprs(List *tlist, bool includeJunk);
 extern int	count_nonjunk_tlist_entries(List *tlist);
 extern bool tlist_same_exprs(List *tlist1, List *tlist2);
 extern bool tlist_same_datatypes(List *tlist, List *colTypes, bool junkOK);
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@ -144,6 +144,7 @@ struct ParseState
 	List	   *p_windowdefs;	/* raw representations of window clauses */
 	ParseExprKind p_expr_kind;	/* what kind of expression we're parsing */
 	int			p_next_resno;	/* next targetlist resno to assign */
 	List	   *p_multiassign_exprs;	/* junk tlist entries for multiassign */
 	List	   *p_locking_clause;		/* raw FOR UPDATE/FOR SHARE info */
 	Node	   *p_value_substitute;		/* what to replace VALUE with, if any */
 	bool		p_hasAggs;
--- a/src/test/regress/expected/update.out
+++ b/src/test/regress/expected/update.out
@ -55,31 +55,80 @@ SELECT * FROM update_test;
 --
 -- Test multiple-set-clause syntax
 --
 INSERT INTO update_test SELECT a,b+1,c FROM update_test;
 SELECT * FROM update_test;
  a  | b  |  c  
 -----+----+-----
 100 | 20 | foo
 100 | 20 | 
 100 | 21 | foo
 100 | 21 | 
 (4 rows)
 UPDATE update_test SET (c,b,a) = ('bugle', b+11, DEFAULT) WHERE c = 'foo';
 SELECT * FROM update_test;
  a  | b  |   c   
 -----+----+-------
 100 | 20 | 
 100 | 21 | 
  10 | 31 | bugle
-(2 rows)
+  10 | 32 | bugle
 (4 rows)
 UPDATE update_test SET (c,b) = ('car', a+b), a = a + 1 WHERE a = 10;
 SELECT * FROM update_test;
  a  | b  |  c  
 -----+----+-----
 100 | 20 | 
 100 | 21 | 
  11 | 41 | car
-(2 rows)
+  11 | 42 | car
 (4 rows)
 -- fail, multi assignment to same column:
 UPDATE update_test SET (c,b) = ('car', a+b), b = a + 1 WHERE a = 10;
 ERROR:  multiple assignments to same column "b"
-- XXX this should work, but doesn't yet:
+-- uncorrelated sub-select:
-UPDATE update_test SET (a,b) = (select a,b FROM update_test where c = 'foo')
+UPDATE update_test
-  WHERE a = 10;
+  SET (b,a) = (select a,b from update_test where b = 41 and c = 'car')
-ERROR:  syntax error at or near "select"
+  WHERE a = 100 AND b = 20;
-LINE 1: UPDATE update_test SET (a,b) = (select a,b FROM update_test ...
+SELECT * FROM update_test;
-                                        ^
+  a  | b  |  c  
 -----+----+-----
 100 | 21 | 
  11 | 41 | car
  11 | 42 | car
  41 | 11 | 
 (4 rows)
 -- correlated sub-select:
 UPDATE update_test o
  SET (b,a) = (select a+1,b from update_test i
               where i.a=o.a and i.b=o.b and i.c is not distinct from o.c);
 SELECT * FROM update_test;
 a  |  b  |  c  
 ----+-----+-----
 21 | 101 | 
 41 |  12 | car
 42 |  12 | car
 11 |  42 | 
 (4 rows)
 -- fail, multiple rows supplied:
 UPDATE update_test SET (b,a) = (select a+1,b from update_test);
 ERROR:  more than one row returned by a subquery used as an expression
 -- set to null if no rows supplied:
 UPDATE update_test SET (b,a) = (select a+1,b from update_test where a = 1000)
  WHERE a = 11;
 SELECT * FROM update_test;
 a  |  b  |  c  
 ----+-----+-----
 21 | 101 | 
 41 |  12 | car
 42 |  12 | car
    |     | 
 (4 rows)
 -- if an alias for the target table is specified, don't allow references
 -- to the original table name
 UPDATE update_test AS t SET b = update_test.b + 10 WHERE t.a = 10;
@ -90,10 +139,12 @@ HINT:  Perhaps you meant to reference the table alias "t".
 -- Make sure that we can update to a TOASTed value.
 UPDATE update_test SET c = repeat('x', 10000) WHERE c = 'car';
 SELECT a, b, char_length(c) FROM update_test;
-  a  | b  | char_length 
+ a  |  b  | char_length 
-----+----+-------------
+----+-----+-------------
- 100 | 20 |            
+ 21 | 101 |            
-  11 | 41 |       10000
+    |     |            
-(2 rows)
+ 41 |  12 |       10000
 42 |  12 |       10000
 (4 rows)
 DROP TABLE update_test;
--- a/src/test/regress/sql/update.sql
+++ b/src/test/regress/sql/update.sql
@ -39,6 +39,9 @@ SELECT * FROM update_test;
 -- Test multiple-set-clause syntax
 --
 INSERT INTO update_test SELECT a,b+1,c FROM update_test;
 SELECT * FROM update_test;
 UPDATE update_test SET (c,b,a) = ('bugle', b+11, DEFAULT) WHERE c = 'foo';
 SELECT * FROM update_test;
 UPDATE update_test SET (c,b) = ('car', a+b), a = a + 1 WHERE a = 10;
@ -46,9 +49,22 @@ SELECT * FROM update_test;
 -- fail, multi assignment to same column:
 UPDATE update_test SET (c,b) = ('car', a+b), b = a + 1 WHERE a = 10;
-- XXX this should work, but doesn't yet:
+-- uncorrelated sub-select:
-UPDATE update_test SET (a,b) = (select a,b FROM update_test where c = 'foo')
+UPDATE update_test
-  WHERE a = 10;
+  SET (b,a) = (select a,b from update_test where b = 41 and c = 'car')
  WHERE a = 100 AND b = 20;
 SELECT * FROM update_test;
 -- correlated sub-select:
 UPDATE update_test o
  SET (b,a) = (select a+1,b from update_test i
               where i.a=o.a and i.b=o.b and i.c is not distinct from o.c);
 SELECT * FROM update_test;
 -- fail, multiple rows supplied:
 UPDATE update_test SET (b,a) = (select a+1,b from update_test);
 -- set to null if no rows supplied:
 UPDATE update_test SET (b,a) = (select a+1,b from update_test where a = 1000)
  WHERE a = 11;
 SELECT * FROM update_test;
 -- if an alias for the target table is specified, don't allow references
 -- to the original table name