Bruno Wolff III <bruno@xxxxxxxx> writes: > Rajesh Kumar Mallah <mallah.rajesh@xxxxxxxxx> wrote: >> create unique index ab on t(a,b); >> create index b on t(b); > If the b data is large you might get some performance increase from adding > an index on just a. You will be trading off increased work when doing updates > to handle the extra index versus faster searches in a more compact index. This is covered in some detail in TFM: http://www.postgresql.org/docs/8.2/static/indexes-multicolumn.html http://www.postgresql.org/docs/8.2/static/indexes-bitmap-scans.html regards, tom lane
