Re: Indexs and prolems with.

On Wed, 6 Feb 2002, Michael McAlpine wrote:

> Here are the results and the puzzle
>
> 1)  explain select * from table1 where charcol1 = 'asdfasd'
>      Index Scan using idx_charcol1  on table1  (cost=0.00..5.00 rows=1 width=456)
>
> 2)  explain select * from table1 where charcol1 like 'asdfa%'
>      Index Scan using idx_charcol1 on table1  (cost=0.00..5.00 rows=1 width=456)
>
> 3)  explain select * from table1 where charcol2 like "aefsadf%'
>      Index Scan using idx_charcol2 on table1  (cost=0.00..5.00 rows=1 width=456)
>
> but when I try
>
> 4)   explain select * from table1 where charcol2  = 'asdfasd'
>      Seq Scan on table1  (cost=0.00..234872.84 rows=168205 width=456)
>
>
> I have the proper locale setting for like queries ("C") and have
> recreated the indexes and vacuum analyzed but cannot get the last
> query to use the index.

How many rows are in the table?  It's estimating 168205 rows matching
asdfasd which could very possibly push it over to deciding on a sequence
scan.