Difficulty getting a count

Question

Given a table that looks like this:
ALLOC_NUMBER ALLOC_PCT
88888 2.71428571
88888 0
87777 -2.7142857
85555 11.0429273
I want to group by alloc_number and determine if the sum of the alloc_pct in that group is > 0. If so, return a count of all alloc_numbers in the table that satisfy that condition, w/o duplicates.
If I write:
SELECT alloc_number
FROM alloc_transfer
GROUP BY alloc_number
HAVING     SUM(alloc_pct) > 0;
It lists the alloc numbers that I want to count, but how do I get the count instead? Just adding COUNT to the Select clause will not work because that will give a count within the group, not for the whole table.
Thanks.
Edited by: Prohan on Feb 8, 2010 2:39 PM

Answer 1

Hi,
Prohan wrote:
As an aside, it looks like it doesn't even matter what the inner aggregate function is; i. e., I could have written:
SELECT COUNT (SUM(alloc_pct))
FROM alloc_transfer
GROUP BY alloc_number
HAVING SUM(alloc_pct) > 0;
The point is simply to bring back a result, any result, for the GROUP of alloc_numbers. Then the outer aggregate function simply counts the number of results that were returned by the inner one; the number of results being equivalent, of course, to the number of alloc_numbers, which is what I'm trying to count.Exactly!
The argument to COUNT must be an aggregate function. Any aggregate function will do, but be careful if it can return NULL.
For example, if you had a column called comment_txt that was almost always NULL, then you wouldn't want the inner aggregate function to be MAX (comment_txt); if every row in a group had NULL comment_txt, then MAX (comment_txt) would be NULL, and the group would not get counted, regardless of alloc_pct.
I chose COUNT for the inner aggregate function, because it never returns NULL. COUNT ignores NULLs, but if it encounters nothing except NULLs, it returns 0, not NULL.
SUM can return NULL, but it's okay to use "SUM (alloc_pct)" in this query, because, if it happened to be NULL, the row would be discarded by the HAVING clause.
Knowing that, can you think of a way to make the query even shorter?
Lose the HAVING clause.
If the SELECT clause is "SELECT COUNT (SUM(alloc_pct))", then the results will be the same if we omit "HAVING SUM(alloc_pct) > 0". The rows discarded by that HAVING clause won't be counted anyway.
Edited by: Frank Kulash on Feb 9, 2010 12:54 PM