Subject RE: [firebird-support] Nested aggregate functions Rick Debay 2007-02-22T16:12:53Z
The query was only an example to demonstrate the problem. The actual
query is quite different.
From what I infer, a nested aggregation isn't possible as there is no
way to define sub-groupings under the original GROUP BY.
In the given example, the subSELECT should be evaluated for every row,
and be oblivious to the grouping.

-----Original Message-----
From: firebird-support@yahoogroups.com
[mailto:firebird-support@yahoogroups.com] On Behalf Of Svein Erling
Tysvaer
Sent: Thursday, February 22, 2007 4:11 AM
To: Firebird-support
Subject: Re: [firebird-support] Nested aggregate functions

Rick Debay wrote:
> I think the test for nested aggregate functions is incorrect.
> The following statement is allowed:
>
> SELECT
> SUM(t1.COL1 - (SELECT t2.COL1 FROM TABLE2 t2 WHERE t2.COL2 = ?))
> FROM
> TABLE1 t1
>
> This statement is not (returns 'Nested aggregate functions are not
> allowed'):
>
> SELECT
> SUM(t1.COL1 - (SELECT SUM(t2.COL1) FROM TABLE2 t2 WHERE t2.COL2 =
> ?)) FROM
> TABLE1 t1
>
> In both cases the SELECT on TABLE2 is standalone, and does not require

> any nested aggregation on the original stream.

Hi Rick, I'm answering since no-one else have done so.

I've never tried doing anything like this, but to me it seems like a
nested aggregation since you want the sum of t2.COL1 to be subtracted
from every individual t1.COL1.

Suppose you had these values:

Table1
COL1
2
4

Table2 (ignoring COL2 for now)
COL1
1
3

Doing your calculation would mean

2-(1+3)+4-(1+3)

and I consider (1+3) to be a nested aggregation.

Moreover, I would expect your particular calculation to be equivalent to

SELECT
SUM(t1.COL1) -
(SELECT SUM(t2.COL1) FROM TABLE2 t2 WHERE t2.COL2 = ?) * (SELECT
COUNT(*) FROM TABLE1 t1a) //or simply COUNT(*)?
FROM
TABLE1 t1

to work (even though I haven't tried it).

Set

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