Add OLD/NEW support to RETURNING in DML queries.

This allows the RETURNING list of INSERT/UPDATE/DELETE/MERGE queries
to explicitly return old and new values by using the special aliases
"old" and "new", which are automatically added to the query (if not
already defined) while parsing its RETURNING list, allowing things
like:

  RETURNING old.colname, new.colname, ...

  RETURNING old.*, new.*

Additionally, a new syntax is supported, allowing the names "old" and
"new" to be changed to user-supplied alias names, e.g.:

  RETURNING WITH (OLD AS o, NEW AS n) o.colname, n.colname, ...

This is useful when the names "old" and "new" are already defined,
such as inside trigger functions, allowing backwards compatibility to
be maintained -- the interpretation of any existing queries that
happen to already refer to relations called "old" or "new", or use
those as aliases for other relations, is not changed.

For an INSERT, old values will generally be NULL, and for a DELETE,
new values will generally be NULL, but that may change for an INSERT
with an ON CONFLICT ... DO UPDATE clause, or if a query rewrite rule
changes the command type. Therefore, we put no restrictions on the use
of old and new in any DML queries.

Dean Rasheed, reviewed by Jian He and Jeff Davis.

Discussion: https://postgr.es/m/CAEZATCWx0J0-v=Qjc6gXzR=KtsdvAE7Ow=D=mu50AgOe+pvisQ@mail.gmail.com

1 files changed, 47 insertions, 0 deletions

diff --git a/src/backend/optimizer/util/paramassign.c b/src/backend/optimizer/util/paramassign.c
index 8e089c27070..3bd3ce37c8f 100644
--- a/src/backend/optimizer/util/paramassign.c
+++ b/src/backend/optimizer/util/paramassign.c
@@ -91,6 +91,7 @@ assign_param_for_var(PlannerInfo *root, Var *var)
 				pvar->vartype == var->vartype &&
 				pvar->vartypmod == var->vartypmod &&
 				pvar->varcollid == var->varcollid &&
+				pvar->varreturningtype == var->varreturningtype &&
 				bms_equal(pvar->varnullingrels, var->varnullingrels))
 				return pitem->paramId;
 		}
@@ -359,6 +360,52 @@ replace_outer_merge_support(PlannerInfo *root, MergeSupportFunc *msf)
 }
 
 /*
+ * Generate a Param node to replace the given ReturningExpr expression which
+ * is expected to have retlevelsup > 0 (ie, it is not local).  Record the need
+ * for the ReturningExpr in the proper upper-level root->plan_params.
+ */
+Param *
+replace_outer_returning(PlannerInfo *root, ReturningExpr *rexpr)
+{
+	Param	   *retval;
+	PlannerParamItem *pitem;
+	Index		levelsup;
+	Oid			ptype = exprType((Node *) rexpr->retexpr);
+
+	Assert(rexpr->retlevelsup > 0 && rexpr->retlevelsup < root->query_level);
+
+	/* Find the query level the ReturningExpr belongs to */
+	for (levelsup = rexpr->retlevelsup; levelsup > 0; levelsup--)
+		root = root->parent_root;
+
+	/*
+	 * It does not seem worthwhile to try to de-duplicate references to outer
+	 * ReturningExprs.  Just make a new slot every time.
+	 */
+	rexpr = copyObject(rexpr);
+	IncrementVarSublevelsUp((Node *) rexpr, -((int) rexpr->retlevelsup), 0);
+	Assert(rexpr->retlevelsup == 0);
+
+	pitem = makeNode(PlannerParamItem);
+	pitem->item = (Node *) rexpr;
+	pitem->paramId = list_length(root->glob->paramExecTypes);
+	root->glob->paramExecTypes = lappend_oid(root->glob->paramExecTypes,
+											 ptype);
+
+	root->plan_params = lappend(root->plan_params, pitem);
+
+	retval = makeNode(Param);
+	retval->paramkind = PARAM_EXEC;
+	retval->paramid = pitem->paramId;
+	retval->paramtype = ptype;
+	retval->paramtypmod = exprTypmod((Node *) rexpr->retexpr);
+	retval->paramcollid = exprCollation((Node *) rexpr->retexpr);
+	retval->location = exprLocation((Node *) rexpr->retexpr);
+
+	return retval;
+}
+
+/*
  * Generate a Param node to replace the given Var,
  * which is expected to come from some upper NestLoop plan node.
  * Record the need for the Var in root->curOuterParams.