On 6/25/23 10:01, Marc Millas wrote:
> Hi,
>
> I have had a perf (++) pb with a join plan cf the pb with join plan thread.
> I did simplify the thing up to when its a simple join between a 15M lines
> table and a 30k lines table.
> if I put in the on part something like table1.a=table2.b, Postgres does
> the job in around 1 seconde.
>
> if in the on part of the join I write table1.a=table2.b OR
> substr(table1.c,x,x) =table2.d
That left side SUBSTR() can't be good for the query optimizer. (Or I'm old
and still using habits picked up 25 years ago on a different RDBMS.)
Maybe a function index on table1 would help.
--
Born in Arizona, moved to Babylonia.