Re: Question about index usage

Guido Neitzer <guido.neitzer@pharmaline.de> writes:
> Is there a reason why this query:
> select id from dga_dienstleister where plz in ('45257', '45259');
> doesn't use this index:
>      "dga_dienstleister_plz_index" btree (plz varchar_pattern_ops)
> but uses this index:
>      "dga_dienstleister_plz_index2" btree (plz)

Because IN means "=", which is a member of the index opclass for the
second index but not the first.

Why do you care?  Should be about the same result either way.

            regards, tom lane