| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com> |
| Cc: | Γιωργος Βαλκανας <lebiathan(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: "SELECT .. WHERE NOT IN" query running for hours |
| Date: | 2011-01-14 19:01:23 |
| Message-ID: | AANLkTimPFtZzR=L_fztok-xcKiQYvgQAiFt=AtY8_9+U@mail.gmail.com |
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| Lists: | pgsql-performance |
2011/1/10 Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>:
> Well, I really hoped that Bruce, Robert or Greg would take on this one, but
> since there are no more qualified takers, I'll take a shot at this one. For
> the "NOT IN (result of a correlated sub-query)", the sub-query needs to be
> executed for every row matching the conditions on the driving table, while
> the !EXISTS is just a complement of join. It's all in the basic set theory
> which serves as a model for the relational databases.
As Scott says, the real problem is the NULL handling. The semantics
are otherwise similar.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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