I was doing the explain thing when I discovered my mistake!
The think is that I over simplyfied my examples. instead of searching
for one ID, I was searching for several ids and I forgot to put a
parentesis arround the or like this.
I was doing this:
select *
from file a, file_tag b, tag c
where
I really thought that Postgresql would rewrite a query from
select *
from file a, file_tag b, tag c
where a.id_file=b.id_file and b.id_tag=c.id_tag and a.id_file=100100
to something like:
select *
from (file a inner join file_tag b on (a.id_file=b.id_file)) inner join
tag c on (b.id_tag
