> mydb=# create index str_idx_url on str(url) where url is not null;
> CREATE
> mydb=# analyze str;
> ANALYZE
> mydb=# EXPLAIN ANALYZE select id from str where url='foobar';
> NOTICE: QUERY PLAN:
>
> Seq Scan on str (cost=0.00..91.05 rows=3 width=4) (actual
You can try an index like:
create index str_idx_url on str(url) where url >= '';
I think that should be identical. ('' is the smallest string, no ?)
Andreas