Add RETURNING support to MERGE.

This allows a RETURNING clause to be appended to a MERGE query, to
return values based on each row inserted, updated, or deleted. As with
plain INSERT, UPDATE, and DELETE commands, the returned values are
based on the new contents of the target table for INSERT and UPDATE
actions, and on its old contents for DELETE actions. Values from the
source relation may also be returned.

As with INSERT/UPDATE/DELETE, the output of MERGE ... RETURNING may be
used as the source relation for other operations such as WITH queries
and COPY commands.

Additionally, a special function merge_action() is provided, which
returns 'INSERT', 'UPDATE', or 'DELETE', depending on the action
executed for each row. The merge_action() function can be used
anywhere in the RETURNING list, including in arbitrary expressions and
subqueries, but it is an error to use it anywhere outside of a MERGE
query's RETURNING list.

Dean Rasheed, reviewed by Isaac Morland, Vik Fearing, Alvaro Herrera,
Gurjeet Singh, Jian He, Jeff Davis, Merlin Moncure, Peter Eisentraut,
and Wolfgang Walther.

Discussion: http://postgr.es/m/CAEZATCWePEGQR5LBn-vD6SfeLZafzEm2Qy_L_Oky2=qw2w3Pzg@mail.gmail.com

1 files changed, 11 insertions, 8 deletions

diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 7f23d18b370..40ea19e6f10 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -72,7 +72,6 @@ static void determineRecursiveColTypes(ParseState *pstate,
 									   Node *larg, List *nrtargetlist);
 static Query *transformReturnStmt(ParseState *pstate, ReturnStmt *stmt);
 static Query *transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt);
-static List *transformReturningList(ParseState *pstate, List *returningList);
 static Query *transformPLAssignStmt(ParseState *pstate,
 									PLAssignStmt *stmt);
 static Query *transformDeclareCursorStmt(ParseState *pstate,
@@ -551,7 +550,8 @@ transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 	qual = transformWhereClause(pstate, stmt->whereClause,
 								EXPR_KIND_WHERE, "WHERE");
 
-	qry->returningList = transformReturningList(pstate, stmt->returningList);
+	qry->returningList = transformReturningList(pstate, stmt->returningList,
+												EXPR_KIND_RETURNING);
 
 	/* done building the range table and jointree */
 	qry->rtable = pstate->p_rtable;
@@ -978,7 +978,8 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 	/* Process RETURNING, if any. */
 	if (stmt->returningList)
 		qry->returningList = transformReturningList(pstate,
-													stmt->returningList);
+													stmt->returningList,
+													EXPR_KIND_RETURNING);
 
 	/* done building the range table and jointree */
 	qry->rtable = pstate->p_rtable;
@@ -2454,7 +2455,8 @@ transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt)
 	qual = transformWhereClause(pstate, stmt->whereClause,
 								EXPR_KIND_WHERE, "WHERE");
 
-	qry->returningList = transformReturningList(pstate, stmt->returningList);
+	qry->returningList = transformReturningList(pstate, stmt->returningList,
+												EXPR_KIND_RETURNING);
 
 	/*
 	 * Now we are done with SELECT-like processing, and can get on with
@@ -2551,10 +2553,11 @@ transformUpdateTargetList(ParseState *pstate, List *origTlist)
 
 /*
  * transformReturningList -
- *	handle a RETURNING clause in INSERT/UPDATE/DELETE
+ *	handle a RETURNING clause in INSERT/UPDATE/DELETE/MERGE
  */
-static List *
-transformReturningList(ParseState *pstate, List *returningList)
+List *
+transformReturningList(ParseState *pstate, List *returningList,
+					   ParseExprKind exprKind)
 {
 	List	   *rlist;
 	int			save_next_resno;
@@ -2571,7 +2574,7 @@ transformReturningList(ParseState *pstate, List *returningList)
 	pstate->p_next_resno = 1;
 
 	/* transform RETURNING identically to a SELECT targetlist */
-	rlist = transformTargetList(pstate, returningList, EXPR_KIND_RETURNING);
+	rlist = transformTargetList(pstate, returningList, exprKind);
 
 	/*
 	 * Complain if the nonempty tlist expanded to nothing (which is possible