[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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