I fail to see the point of DEALLOCATE IF EXISTS. Do you have real use case for this, or was this just a case of adding IF EXISTS to all commands for the sake of completeness?
Usually the client knows what statements have been prepared, but perhaps you want to make sure everything is deallocated in some error handling case or similar. But in that case, you might as well just issue a regular DEALLOCATE and ignore errors. Or even more likely, you'll want to use DEALLOCATE ALL.
Hmm. The test case I had for it, which was very annoying in an "I want to be lazy" sort of way, I am unable to reproduce now. So I guess this becomes a "make it like the others" and the community can decide whether that's desirable.
In my personal case, which again I can't reproduce because it's been a while since I've done it, DEALLOCATE ALL would have worked. I was basically preparing a query to work on it in the same conditions that it would be executed in a function, and I was only working on one of these at a time so ALL would have been fine.
