Hi, you maybe don't know that questions get more attention when some effort is provided in asking them.

Remember that nobody else can see your screen or know what you are thinking, trying to do and what you are working with. What you don't describe is unknown, and when there is too much unknown no reply is posted.

On a different point: don't you think a good practice would already be to avoid executing unnecessary operations?

CASE WHEN <something> is null THEN y ELSE n END = y : can you think of a more direct and simpler (= quicker) way to write that condition? Doing a IF-ELSE to then check for one of the values is a waste of time. You already know the condition as it's written in the IF-ELSE, so use that condition directly.

Now thinking at your error: an aggregate is not allowed in the USING clause of a FILTER operator. Is your "Workload (k$)" an aggregate? If it is, well, the message is explicit: it isn't allowed there. The USING clause only takes attributes, not aggregated measures.