Hello,
Consider the following query:
select t1field1, avg(t2fieild2)
from t1, t2
where t1.field1 = t2.field2
group by t1field1
That works fine. But I'd really like to see more fields of t1 in this
query, however I can't add them into the select because they're not
part of the GROUP BY, thus I have to add them to there too:
select t1field1, t1field2, t1field3, avg(t2fieild2)
from t1, t2
where t1.field1 = t2.field2
group by t1field1, t1field2, t1field3
The problem is that addind them all to GROUP BY causes a performance
loss.. The only solution I found is using a subquery like this:
select * from
t1, (select t1field1, avg(t2fieild2)
from t1, t2
where t1.field1 = t2.field2
group by t1field1) t1inner
where t1.field1 = t1inner.field1
It works just fine.. But I prefer not to use subqueries unless I am
really forced to due to the design of my application.
Another solution I considered is using aggreate function like that:
select t1field1, max(t1field2), max(t1field3), avg(t2fieild2)
from t1, t2
where t1.field1 = t2.field2
group by t1field1
Sadly, this caused the same performance... I wonder though, is it
possible to make an aggregate function like first(), last() in Oracle
(IIRC)? I believe that in such cases MySQL does first() by itself.
Other ideas are welcome too.
Regards,
Vitaly Belman
ICQ: 1912453
AIM: VitalyB1984
MSN: tmdagent@hotmail.com
Yahoo!: VitalyBe
