Alvaro Herrera <alvherre@xxxxxxxxxxxxxx> writes: > On Mon, Sep 12, 2005 at 09:43:57AM -0400, Reid Thompson wrote: >> Example: >> assume a table of 10 columns, three of which are fname, lname, and dob. >> If an index is created on (fname, lname, dob), will a query that >> utilizes two of the columns ( select 'data' from table where fname = 'X' >> and lname = 'Y') utilize the index? > Yes, if it is selective enough. (It _can_ use the index, which does not > mean that it _will_ use it.) Note that if your example query used the > columns (lname, dob), the answer would be "no." Actually, that last point is not true anymore as of 8.1 --- see this thread: http://archives.postgresql.org/pgsql-hackers/2005-05/msg00939.php which led to this patch: http://archives.postgresql.org/pgsql-committers/2005-06/msg00156.php I missed the fact that the documentation said it wouldn't work though. Will fix... regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
