"postgresql" <postgres@lg.ndirect.co.uk> writes:
> I want to remove all entries from AA where keyA matches that from
> obsolete_AA_entries,
> i.e. SELECT * FROM AA NATURAL JOIN obsolete_AA_entries;
> DELETE FROM AA WHERE EXISTS(
> SELECT * from obsolete_AA_entries o where AA.keyA = o.keyA);
> seems to be faster than
> DELETE FROM AA where (keyA) in (SELECT * from obsolete_AA_entries);
> However, both are sequentially going through AA which is huge rather than
> looking up values one by one from obsolete_AA_entries which is small.
> How do I persuade the database to change its query strategy?
TryDELETE FROM AA WHERE AA.keyA = obsolete_AA_entries.keyA;
This is not valid SQL according to the SQL standard, but Postgres takes
it anyway.
Turning sub-SELECT queries into plannable joins is on the todo list,
but it's not done yet :-(
regards, tom lane