Re: How bad is using queries with thousands of values for operators IN or ANY? - Mailing list pgsql-general

Thorsten Schöning schrieb am 31.08.2020 um 12:37:
> So for what query size or number of IDs to compare in IN would you
> consider a different approach at all?


In my experience "hundreds" of IDs tend to be quite slow if used with an IN clause.

Rewriting the IN to a JOIN against a VALUES clause is very often faster:

So instead of:

  select *
  from t
  where id in (1,2,3, .... ,500);

using this:

  select *
  from t
    join (
       values (1),(2),(3),...(500)
    ) as x(id) on x.id = t.id

produces more often than not a more efficient execution plan (assuming no values are duplicated in the IN list)

Obviously I don't know if such a re-write is even feasible though.

Thomas