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

I think the answer is pretty simple (unless I'm missing something?)

SELECT    
CASE
    WHEN col1 > col2 THEN SUM(col3*col4)
    ELSE 0
END AS some_product
FROM some_table
GROUP BY
CASE
    WHEN col1 > col2 THEN SUM(col3*col4)
    ELSE 0
END

You can put the CASE STATEMENT in the GROUP BY verbatim (minus the alias column name)