I'm trying to get the Product of all rows for a specific column in a grouped by query. Most examples I've found point me towards combining `exp`, `sum` and `log`
exp(sum(log([Column A])))
The problem I'm having is that the column contains some zeros for values and thus I'm getting this error when zeros get passed to the `log` function:
>An invalid floating point operation occurred.
I thought I could work around this by using a `case` expression, but that just doesn't work the way I would think it should, as it seems to evaluate all cases...
select
Name,
Product = case
when min([Value]) = 0 then 0
when min([Value]) <> 0 then exp(sum(log(I))) -- trying to get the product of all rows in this column
end
from ids
group by Name
[SqlFiddle](http://sqlfiddle.com/#!6/5e18f/1)
Given the following result set:
Id Name Value
_________________________________
1 a 1
2 a 2
3 b 0
4 b 1
I would expect to get the following rows:
Name Product
_____________
a 2
b 0
So in summary...
How do you multiply rows in a column that can contain negative or zero valued numbers?
TopAnswers
Databases
Top Answer
meme (imported from SE)
The magic of [NULLIF][1] seems to do the trick for the test case in your question. Since you used a different example than in your SQL Fiddle, I don't know if that's what you want there too.
CREATE TABLE dbo.Ids
(
Id INT NOT NULL IDENTITY(1, 1),
Value INT,
Name NVARCHAR(3)
);
INSERT INTO dbo.Ids ( Name, Value )
VALUES ( 'a', 1 );
INSERT INTO dbo.Ids ( Name, Value )
VALUES ( 'a', 2 );
INSERT INTO dbo.Ids ( Name, Value )
VALUES ( 'b', 0 );
INSERT INTO dbo.Ids ( Name, Value )
VALUES ( 'b', 1 );
SELECT Name,
CASE WHEN MIN(Value) = 0 THEN 0
WHEN MIN(Value) > 0 THEN EXP(SUM(LOG(NULLIF(Value, 0)))) -- trying to get the product of all rows in this column
END AS Product
FROM Ids
GROUP BY Name;
Returns:
Name Product
a 2
b 0
---
If you need a more general solution that handles negative numbers and other edge cases, see for example [The Product Aggregate in T-SQL Versus the CLR][2] by Scott Burkow. One T-SQL construction from that article is:
EXP(SUM(LOG(NULLIF(ABS([Value]), 0))))
*
IIF(SUM(IIF([Value] = 0, 1, NULL)) > 0, 0, 1)
*
IIF(SUM(IIF([Value] < 0, 1, 0)) % 2 = 1, -1, 1)
---
As to why your original `CASE` expression did not work as expected, from the documentation for [CASE (Transact-SQL)][3] (emphasis added):
>You should only depend on order of evaluation of the WHEN conditions for scalar expressions (including non-correlated sub-queries that return scalars), **not for aggregate expressions**.
[1]: https://docs.microsoft.com/en-us/sql/t-sql/language-elements/nullif-transact-sql
[2]: https://www.codeproject.com/Articles/548395/The-Product-Aggregate-in-T-SQL-Versus-the-CLR
[3]: https://docs.microsoft.com/en-us/sql/t-sql/language-elements/case-transact-sql#remarks