GROUP BY question

[Anon]

Can someone tell me what GROUP BY is good for...

thanx in advance

[Anon]

RTFM.
Group by is good for grouping :-)

Say you have a table full of records that contain emails.
Now you want to count how many emails you have had from each unique sender:
SELECT count(*),Sender FROM email_table GROUP BY Sender.

That will do the count(*) on each group of records that have the same Sender.

[Anon]

Another useful thing to do with group by is to do mathmatical stuff on records, like test scores and such.

select name, count(score), sum(score), avg(score) from tests group by name

will return the average someone scored on all tests, as well as the total of all tests added together and how many test scores are in the database.