[thelist] Calculating weighted averages
Bill Moseley
moseley at hank.org
Sat Jul 14 16:55:13 CDT 2007
On Sat, Jul 14, 2007 at 04:13:03PM -0400, r937 wrote:
> if a student has not taken a particular exam, there will be no row in the
> test table for that student for that exam
>
> thus, since it's a LEFT OUTER JOIN, all columns from the test table in the
> query will be null for this situation
>
> consequently, computation involving test.score will be null too
That's what I was hoping for. But,
=> select * from foo; i
----
23
50
(3 rows)
Note last row is NULL.
> select AVG( i ) from foo;
avg
---------------------
36.5000000000000000
(1 row)
So if one row is NULL AVG() is acting on just the non-null rows.
--
Bill Moseley
moseley at hank.org
More information about the thelist
mailing list