On Fri, Dec 18, 2009 at 12:26 AM, Scott Marlowe <scott.marl...@gmail.com>wrote:
> On Thu, Dec 17, 2009 at 4:22 PM, Karl Larsson <karl.larsso...@gmail.com> > wrote: > > Hello. > > > > I have a problem I don't understand. I hope it's a simple problem and I'm > > just stupid. > > > > When I make a subquery Postgres don't care about my indexes and makes > > a seq scan instead of a index scan. Why? > > PostgreSQL uses an intelligent query planner that predicets how many > rows it will get back for each plan and chooses accordingly. Since a > few dozen rows will all likely fit in the same block, it's way faster > to sequentially scan the table than to use an index scan. > > Note that pgsql always has to go back to the original table to get the > rows anyway, since visibility info is not stored in the indexes. > I forgot to mention that I have a reel problem with 937(and growing) rows of data. My test tables and test query is just to exemplify my problem. But I'll extend table_two and see if it change anything. / Karl Larsson
