Re: Why does not perform index combination

"Adnan DURSUN" <a_dursun(at)hotmail(dot)com> writes:
> I have query for a report. Explain analyze result is below. The =
> execution plan tells that it would use "t_koltuk_islem_pkey" index on =
> table "t_koltuk_islem" to scan. However, there is another index on table =
> "t_koltuk_islem" on column "islem_tarihi" that can be combined on plan. =
> Why doesn't optimizer choice that ? It prefer to perform a filter on =
> column "islem_tarihi" ... Why ?

Probably thinks that the extra index doesn't add enough selectivity to
be worth scanning. It's probably right, too --- maybe with a narrower
date range the answer would be different.

I think the main problem in this plan is the poor estimation of the size
of the d1/s join. Are your stats up to date on those tables? Maybe
boosting the statistics target for one or both would help.

regards, tom lane