RE: Sql Question

I'd say half right but for a slightly different reason. Aggregate functions
do not result in NULL in DB2. They may result in NULL in other SQL
implementations. Charles has pointed out below that NULL are skipped from
consideration, rather than nulling the result.

Charles points out below that the result is not NULL, but doesn't emphasize
the fact.

Dennis Lovelady
http://www.linkedin.com/in/dennislovelady
--
"A celebrity is a person who works hard all his life to become well known,
and then wears dark glasses to avoid being recognized."
-- Fred Allen

Half correct.

Comparisons to NULL do result in NULL, which is neither TRUE or FALSE.
Thus the reason the rows are not being returned as expected.

However, aggregate functions skip NULL. The manual puts it like so,
"The function is applied to the set of values derived from the
argument values by the elimination of null values."

So AVG() over FLD1 in the following:
KEY1 FLD1
1 2
2 2
3 3
4 NULL
5 5

Is 3, not 2.4.

AVG({2,2,3,NULL,5}) = AVG({2,2,3,5}) = 3

HTH,
Charles




On Tue, Aug 17, 2010 at 10:05 PM, Loyd Goodbar <loyd@xxxxxxxxxxxxxx>
wrote:

Let me guess: comparisons to NULL result in NULL. Also aggregate

operations containing NULL result in NULL. --Loyd

On Aug 17, 2010, at 19:04, Alan Campin <alan0307d@xxxxxxxxx> wrote:

As the man said, "Very interesting" . Thanks

On Tue, Aug 17, 2010 at 5:40 PM, Dennis Lovelady

<iseries@xxxxxxxxxxxx>wrote:

Dang. here I sit, corrected.  :)  It was about time, since my last

prior

correction was over ten minutes ago.

From Wikipedia: http://en.wikipedia.org/wiki/Null_%28SQL%29

SELECT *
FROM sometable
WHERE num <> 1;  -- Rows where num is NULL will not be returned,
               -- contrary to many users' expectations.