Re: is this a bug or do I not understand the query planner?

"Rob Prowel"  wrote
> two almost identical queries: one searches for
>
> read in ('N','n')
>
> and the other searches for
>
> read in ('Y','y').
>
> the (explain) SQL statement says that one uses the
> index on the (read) field and the other does a
> sequential table scan.  Why!!!????

With big chance, it is not a bug. As your explain indicates, Yy query is 
estimated only return 1 row while Nn query is estimated to return 2018135 
rows. So for the latter, compared to your table size(I guess), an seqscan is 
more suitable.

Try "explain analyze" to see if the query optimizer gets a right guess. If 
not, run "vacuum full analyze", then check again. If still not, you may want 
to post the results here.

Regards,
Qingqing