SQL GROUP BY CASE statement with aggregate function
-
05-07-2019 - |
Question
I have a column that looks something like this:
CASE
WHEN col1 > col2 THEN SUM(col3*col4)
ELSE 0
END AS some_product
And I would like to put it in my GROUP BY clause, but this seems to cause problems because there is an aggregate function in column. Is there a way to GROUP BY a column alias such as some_product
in this case, or do I need to put this in a subquery and group on that?
Solution
My guess is that you don't really want to GROUP BY
some_product.
The answer to: "Is there a way to GROUP BY
a column alias such as some_product in this case, or do I need to put this in a subquery and group on that?" is: You can not GROUP BY
a column alias.
The SELECT
clause, where column aliases are assigned, is not processed until after the GROUP BY
clause. An inline view or common table expression (CTE) could be used to make the results available for grouping.
Inline view:
select ...
from (select ... , CASE WHEN col1 > col2 THEN SUM(col3*col4) ELSE 0 END AS some_product
from ...
group by col1, col2 ... ) T
group by some_product ...
CTE:
with T as (select ... , CASE WHEN col1 > col2 THEN SUM(col3*col4) ELSE 0 END AS some_product
from ...
group by col1, col2 ... )
select ...
from T
group by some_product ...
OTHER TIPS
While Shannon's answer is technically correct, it looks like overkill.
The simple solution is that you need to put your summation outside of the case
statement.
This should do the trick:
sum(CASE WHEN col1 > col2 THEN col3*col4 ELSE 0 END) AS some_product
Basically, your old code tells SQL to execute the sum(X*Y)
for each line individually (leaving each line with its own answer that can't be grouped).
The code line I have written takes the sum product, which is what you want.
If you are grouping by some other value, then instead of what you have,
write it as
Sum(CASE WHEN col1 > col2 THEN SUM(col3*col4) ELSE 0 END) as SumSomeProduct
If, otoh, you want to group By
the internal expression, (col3*col4)
then
write the group By
to match the expression w/o the SUM
...
Select Sum(Case When col1 > col2 Then col3*col4 Else 0 End) as SumSomeProduct
From ...
Group By Case When col1 > col2 Then col3*col4 Else 0 End
Finally, if you want to group By the actual aggregate
Select SumSomeProduct, Count(*), <other aggregate functions>
From (Select <other columns you are grouping By>,
Sum(Case When col1 > col2
Then col3*col4 Else 0 End) as SumSomeProduct
From Table
Group By <Other Columns> ) As Z
Group by SumSomeProduct