Re: Strange result with "SELECT ... ORDER BY random() LIMIT 1" and JOINs

Etienne Dube <etdube(at)gmail(dot)com> writes:
> This query yields unexpected results (tested under 9.2.4):

> SELECT
> s.car_id,
> s.color_id AS subquery_color_id,
> co.color_id AS join_color_id,
> co.color_name
> FROM
> (
> SELECT
> ca.car_id,
> (
> SELECT color_id
> FROM color
> WHERE ca.car_id = ca.car_id -- dependency added to
> avoid getting the same value for every row in the output
> ORDER BY random()
> LIMIT 1
> ) AS color_id
> FROM
> car ca
> ) s
> LEFT JOIN color co ON co.color_id = s.color_id;

> We can see the equality defined in the LEFT JOIN does not hold true for
> the subquery_color_id and join_color_id column aliases in the output.
> EXPLAIN also shows that the subplan for the inner subquery used to pick
> a random row from the color table appears twice.

I've committed patches to prevent duplication of subplans containing
volatile functions. Thanks for the test case!

regards, tom lane