Re: New CORRESPONDING clause design

Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> Is following use case defined in standard?

> postgres=# SELECT 0 AS x1, 1 AS a, 0 AS x2, 2 AS b, 0 AS x3, -1 AS x3
> UNION ALL CORRESPONDING BY(a,b) SELECT 4 AS b, 0 AS x4, 3 AS a,
> 0 AS x6, -1 AS x6
> UNION ALL CORRESPONDING SELECT 0 AS x8, 6 AS a, -100 AS aa;
> ┌───┐
> │ a │
> ╞═══╡
> │ 1 │
> │ 3 │
> │ 6 │
> └───┘
> (3 rows)

> It depends on order of implementation

> if we do (T1 U T2) U T3 ---> then result is correct,
> but if we do T1 U (T2 U T3) ---> than it should to fail

UNION ALL should associate left-to-right, just like most other binary
operators, so this looks fine to me. Did you check that you get an
error if you put in parens to force the other order?

regards, tom lane