On Tue, 2022-07-12 at 14:25 -0400, MichaelDBA Vitale wrote: > On 07/12/2022 2:13 PM Pierson Patricia L (Contractor) <patricia.l.pierson@xxxxxxx> wrote: > > Do a count on the primary key. Will force index access and you don’t access the entire row which may be very long. > > LIKE : select count(ID) from my_table; > > That is not true: doing the select on the primary key will still result in a table scan, > not an index scan. The heap always gets accessed for select counts. I'd say that both statements are wrong: - count(id) is *slower* than count(*), because it has to check each "id" if it is NULL or not (NULL values are not counted). count(*) is just the SQL standard's weird way of writing a parameterless aggregate; it has nothing to do with the * in "SELECT * FROM ". - Both "SELECT count(id) FROM tab" and "SELECT count(*) FROM tab" can result in an index-only scan. You just need the table to be recently VACUUMed, you need a table that is wide enough that a sequential scan is actually slower than an index-only scan, and perhaps you need "random_page_cost" to be low enough. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
