UNION versus SUB SELECT

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От Robert DiFalco
Тема UNION versus SUB SELECT
Дата
Msg-id CAAXGW-w+pF+8Prk9p9SRYwZ56FboRFj6wkSvCh0xUGpFns6uhA@mail.gmail.com
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Ответы Re: UNION versus SUB SELECT  (desmodemone <desmodemone@gmail.com>)
Список pgsql-performance
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I have found this:

SELECT c.* 
FROM contacts c
WHERE c.id IN ( SELECT p.contact_id FROM phone p WHERE p.addr = ? )
OR c.id IN (SELECT e.contact_id FROM email e WHERE e.addr = ? );

To have a worse plan than:

SELECT * FROM contacts where id IN (
( SELECT c.id FROM contacts c 
JOIN phone p ON c.id = p.contact_id AND p.addr = ? 
UNION
SELECT c.id FROM contacts c 
JOIN email e ON c.id = e.contact_id AND e.addr = ? );

Maybe this is no surprise. But after discovering this my question is this, is there another option I dont' know about that is logically the same that can perform even better than the UNION?

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