Re: Regex query not using index

a final question: why does this syntax do a seq scan + filter:

select * from tablea where fielda = fielda   -or-  select * from
tablea where fielda in (fielda)

while this syntax results in no filter, seq scan only

select * from tablea where 1 = 1

it seems that both where clauses should be ignored by the optimizer-
or am i missing something

On Feb 19, 2008 9:45 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> "Postgres User" <postgres.developer@gmail.com> writes:
> > Yes that works, but the whole point of the exercise is replace many OR
> > statements with 1 regex expression.  So it's not what I'm looking for.
>
> Unfortunately, Postgres is not as intelligent as you are.  There is
> no mechanism to rewrite a multi-branch regex condition into multiple
> indexscans.  I recommend going back to the OR's.
>
>                         regards, tom lane
>