"group by" slow for using "count(distinct some_column)" - a better way?

Question

Hi all,
i have an
select
count(distinct some_column),
from [...]
group by [...];
Which is slowed down for the "*count(distinct some_column)*".
The "group by" aggregates base records.
But the base records have 1:n for some #1 event #n records each.
Some of the #n records fall into group by result record (A), some other into group by result record (B).
But each shall only count +1 per event - disregarding how many of the #n record have fallen into that category.
Is there another (faster) way to count for this?
- thanks!
best regards,
Frank
Edited by: user8704911 on Jun 29, 2011 1:30 AM

Answer 1

Hi Dom,
incidentally i went in the direction you proposed:
I replaced the pl/sql collection with the global temporary table.
But the reason for doing this was a different one:
I recognized, that the group by is much faster, if applied on table or global temporary table.
However i first just moved the data from pl/sql collection to global temporary table in order to apply the group by there.
Then the group by is much faster - but the moving of data from pl/sql collection to global temporary table then took away the time.
So it was not the group by, but in general the read-access to the pl/sql collection (btw, around #65,000 records).
Now having completely replaced the pl/sql collection with global temporary table everything is fine.
cheers,
Frank