Or even better create 3 stored procs to retrieve your data. You are using the "one query fits all via dynamic sql" approach. This is full of issues. It is difficult to maintain, once business rules start diverging you have really complicated code (this sounds the case here), you are running the risk of sql injection (maybe not now but in the future).
The code that Kingston shared will work but breaking this into separate pieces is really the best move in the long run.
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