I'm not saying either of the solutions is right or wrong. Both are just different in terms of the final result. They're just not equivalent.

Whether the current approach works just because of plain luck (or the current data distribution) or if it's really intended needs to get clarified.

But for the taks itself (taking aside the concatenation) your preferred solution is NOT EXISTS?

Is this "usually" the fastest solution for a large table against a small lookup table or is this your preferred method to start with?