On Wed, 2023-02-15 at 10:20 -0600, Ron wrote: > On 2/15/23 02:46, Laurenz Albe wrote: > > Which one is best? > > > CREATE UNIQUE INDEX ix1 ON art (code, etb) > > > or > > > CREATE UNIQUE INDEX ix1 ON art (etb, code) > > > > > > (or its PRIMARY KEY equivalent) > > Both are the same. > > > > There is an old myth that says that you should use the more selective column first > > (which would be "code"), but that is just a myth. > > Only on Postgresql? No, on all relational databases that use B-tree indexes. Look at how many index entries have to be scanned in both cases, and you will see. Yours, Laurenz Albe
