Postgres Pro
Downloads
Home   >   mailing lists

Re: Automatic optimization of IN clauses via INNER JOIN - Mailing list pgsql-performance

From Tom Lane
Subject Re: Automatic optimization of IN clauses via INNER JOIN
Date
Msg-id 2106.1261063973@sss.pgh.pa.us
Whole thread Raw
In response to Automatic optimization of IN clauses via INNER JOIN  (Thomas Hamilton <thomashamilton76@yahoo.com>)
Responses Re: Automatic optimization of IN clauses via INNER JOIN
List pgsql-performance
Tree view 
Thomas Hamilton <thomashamilton76@yahoo.com> writes:
> Apparently the latest version of MySQL has solved this problem:
http://www.xaprb.com/blog/2006/06/28/why-large-in-clauses-are-problematic/
> But I am running PostgreSQL v8.3 and am observing generally that SELECT ... WHERE ... IN (a, b, c, ...) is much
slowerthan SELECT ... INNER JOIN (SELECT a UNION ALL�SELECT b UNION ALL SELECT c ...) 

> Why doesn't the optimizer automatically transform IN clauses to INNER JOINs in this fashion?

Did you read all the comments on that three-year-old article?

            regards, tom lane

pgsql-performance by date:

Previous
From: Thomas Hamilton
Date:
Subject: Automatic optimization of IN clauses via INNER JOIN
Next
From: Thomas Hamilton
Date:
Subject: Re: Automatic optimization of IN clauses via INNER JOIN