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Re: Index on a NULL-value

From: Tobias Brox <tobias(at)nordicbet(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Index on a NULL-value
Date: 2005-05-31 03:21:20
Message-ID: 20050531032119.GH26100@tobias.exoweb.net (view raw or flat)
Thread:
Lists: pgsql-performance
[Tobias Brox - Tue at 11:02:07AM +0800]
> test=# explain select * from mock where b is NULL;
>                              QUERY PLAN                             
> --------------------------------------------------------------------
>  Seq Scan on mock (cost=100000000.00..100000020.00 rows=6 width=8)
>    Filter: (b IS NULL)
> (2 rows)

(...)

> ---------------------------(end of broadcast)---------------------------
> TIP 9: the planner will ignore your desire to choose an index scan if your
>       joining column's datatypes do not match

That tip helped me :-)

test=# explain select * from mock where (b IS NULL)=true;
                              QUERY PLAN                              

----------------------------------------------------------------------
 Index Scan using b_is_null on mock  (cost=0.00..4.68 rows=1 width=8)
   Index Cond: ((b IS NULL) = true)
(2 rows)

-- 
Tobias Brox, Beijing

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