Re: bug or lacking doc hint

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.