Re: [HACKERS] Idea on how to simplify comparing two sets

On Tue, Feb 07, 2017 at 04:13:40PM +0100, Joel Jacobson wrote:
>  Hi hackers,
> 
> Currently there is no simple way to check if two sets are equal.

Assuming that a and b each has at least one NOT NULL column, is this
simple enough?  Based on nothing much, I'm assuming here that the IS
NOT NULL test is faster than IS NULL, but you can flip that and change
the array to {0} with identical effect.

WITH t AS (   SELECT a AS a, b AS b, (a IS NOT NULL)::int + (b IS NOT NULL)::int AS ind   FROM a FULL JOIN b ON ...
)
SELECT array_agg(DISTINCT ind) = '{2}'
FROM t;

Best,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
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