On Mon, 2 Feb 2004, Tomasz Myrta wrote: > Dnia 2004-02-02 19:30, Użytkownik scott.marlowe napisał: > > Not entirely, since it only has to sort two columns, it will be smaller, > > and will therefore be somewhat faster. > > Can you say something more about it? Will it be enough faster to keep > them both? Did anyone make such tests?
that really depends on the distribution of the third column. If there's only a couple of values in the third column, no big deal. If each entry is unique, and it's a large table, very big deal. It is only useful to have a three column index if you actually use it. If you have an index on (a,b,c) and select order by b, the index won't get used unless the a part is in the where clause. the other issue is updates. IT WILL cost more to update two indexes rather than one. Generally, you can drop / readd the index and use explain analyze on one of your own queries to see if that helps. ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html