Gaetano,
> I did in that way just to not use postgresql specific feature.
> I can give it a try and I let you know, however the question remain,
> why the index usage is lost if used in that way ?
Because PostgreSQL is materializing the entire UNION data set in the
subselect. What Postgres version are you using? I thought this was fixed
in 7.4, but maybe not ...
--
Josh Berkus
Aglio Database Solutions
San Francisco