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Date: Wed, 08 Feb 2006 16:27:04 -0500
To: pgsql-sql@postgresql.org
From: Frank Bax <fbax@sympatico.ca>
Subject: Re: Non Matching Records in Two Tables
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At 04:10 PM 2/8/06, Ken Hill wrote:
>I need some help with a bit of SQL. I have two tables. I want to find 
>records in one table that don't match records in another table based on a 
>common column in the two tables. Both tables have a column named 'key100'. 
>I was trying something like:
>
>SELECT count(*)
>FROM table1, table2
>WHERE (table1.key100 != table2.key100);
>
>But the query is very slow and I finally just cancel it. Any help is very 
>much appreciated.


vacuum analyse table1;

vacuum analyse table2;

select count(*) from table1 full outer join table2 on 
table1.key100=table2.key100 where table1.key100 is null or table2.key100 is 
null;

If this is also slow, post output of "EXPLAIN ANALYSE SELECT ...."