Update: The original dev does not remember exactly. However they have said that clientId was originally a VARCHAR, so this may have been checking for both '0' or ''

So an over-engineered workaround to a bad datatype perhaps?

The client table has around 100,000 rows each with a unique clientId, none of which are returned from the CAST / ABS / SIN

I think you are right and this is a ‘fix’ for something lost to time. I am going to talk to the original dev tomorrow to see if they remember what it was for