Re: [DEPARSE] EXPLAIN prints another ModifyTable's RETURNING aliases in a SubPlan

Hi Tom, Dean,

> This makes me think it is probably possible to construct scenarios
> where a plan contains both VAR_RETURNING Vars that originated inside
> a rule and some that originated from the calling query, in which
> case using either level's aliases across-the-board would be wrong.

Here is one. With your fragment, the EXPLAIN below prints
"Output: n.a, n.a", although the two columns are the old and new
values (1 and 101). Current master and Ayush's patch print
"Output: n.a, new.a".

CREATE TABLE t (a int, b int);
INSERT INTO t VALUES (1, 10);
CREATE VIEW v AS SELECT * FROM t;
CREATE RULE v_upd AS ON UPDATE TO v DO INSTEAD
UPDATE t SET a = new.a, b = new.b WHERE a = old.a
RETURNING WITH (NEW AS n) n.a, n.b;
EXPLAIN (VERBOSE, COSTS OFF)
UPDATE v SET a = a + 100
RETURNING WITH (OLD AS n) n.a AS old_a, new.a AS new_a;

The calling query names OLD "n" and the rule names NEW "n", so with
the rule's aliases preferred the two sides get the same name.

Best regards,
Henson