Re: optimizing large query with IN (...)

On Wed, Mar 10, 2004 at 02:02:23PM -0300, Marcus Andree S. Magalhaes wrote:

> Hmm... from the 'performance' point of view, since the data comes from
> a quite complex select statement, Isn't it better/quicker to have this
> select replaced by a select into and creating a temporary database?

Definitely - why loop the data into the application and back out again
if you don't need to?

> > The problem, as I understand it, is that 7.4 introduced massive
> > improvements in handling moderately large in() clauses, as long as they
> > can fit in sort_mem, and are provided by a subselect.
> >
> > So, creating a temp table with all the values in it and using in() on
> > the  temp table may be a win:
> >
> > begin;
> > create temp table t_ids(id int);
> > insert into t_ids(id) values (123); <- repeat a few hundred times
> > select * from maintable where id in (select id from t_ids);
> > ...

Cheers,
  Steve