Re: Broken type checking for empty subqueries

On 9/28/23 11:08, Marek Malevič wrote:
> Hello,
>
> after upgrade from PG11 to PG14.8 the following statement started failing:
>
> select
>     a::BIGINT
> FROM (
>     SELECT
>         '$maybeNumber'::VARCHAR AS a
>     WHERE NOT '$maybeNumber' LIKE '%maybeNumber'
> ) AS foo;
>
> Expected (as in PG11): The query should return empty result with one
> column.
> Actual:  SQL Error [22P02]: ERROR: invalid input syntax for type bigint:
> "$maybeNumber".
>
> Where is a workaround that shows the behavior is quite non-stable.
> Following passes normally while still using the same subquery with one
> more empty result from another one:
>
> select
>     a::BIGINT
> FROM (
>     SELECT
>         '$maybeNumber'::VARCHAR AS a
>     WHERE NOT '$maybeNumber' LIKE '%maybeNumber'
>     UNION
>     SELECT '0' AS a WHERE false
> ) AS foo;

I bisected this back to 4be058fe9ec5e630239b656af21fc083371f30ed, "In
the planner, replace an empty FROM clause with a dummy RTE."
--
Vik Fearing