Re: Constraint on multicolumn index - Mailing list pgsql-sql

From Tom Lane
Subject Re: Constraint on multicolumn index
Date
Msg-id 20924.1163171264@sss.pgh.pa.us
Whole thread Raw
In response to Constraint on multicolumn index  ("Stuart Brooks" <stuartb@cat.co.za>)
List pgsql-sql
"Stuart Brooks" <stuartb@cat.co.za> writes:
> But if I want the next item following t=(a=10,b=100,c=1000):

>  select * from T
>  where (a=10 AND b=100 AND c>1000) OR (a=10 AND b>100) OR (a>10)
>  order by a,b,c;

The correct way to handle this is to use a SQL-spec row comparison:
where (a,b,c) > (10,100,1000)

Unfortunately, that syntax does not work per-spec in any existing
Postgres release.  It will work properly (and use the index) in
PG 8.2, for what that's worth.

Not sure if there's any reasonable workaround in PG <= 8.1.
You might want to check this old thread:
http://archives.postgresql.org/pgsql-performance/2004-07/msg00188.php
(note that none of the first few responses got the point :-()  Also
http://archives.postgresql.org/pgsql-hackers/2006-02/msg00209.php
        regards, tom lane


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