SQL GROUP BY CASE statement with aggregate function

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

Answer 1

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(*), 
From (Select , 
      Sum(Case When col1 > col2 
          Then col3*col4 Else 0 End) as SumSomeProduct
      From Table
      Group By  ) As Z
Group by SumSomeProduct