The most efficient way to put this?

The query I'd like to run is fairly simple. Unfortunately, PG doesn't handle
IN's very well.

SELECT DISTINCT ON (aa.a) aa.a, aa.b, aa.c FROM aa WHERE aa.a NOT IN (select
zz.a from zz);

This is with two very large tables. Both zz and aa have many millions of
rows.

The best I've come up with so far is...

 SELECT DISTINCT ON (aa.a) aa.a, aa.b, aa.c FROM aa WHERE NOT EXISTS (SELECT
zz.a FROM zz WHERE aa.a = zz.a);

Does anyone have anything better?

--Arsalan

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People often hate those things which they do not know, or cannot understand.
--Ali Ibn Abi Talib (A.S.)