Well, it got me at least! Not long ago someone asked me about partitioned views and as I'm apt to do, I just did a demo on the fly. I built two tables, added the check constraints, then union all'd them together in a view. But the query showed both tables being queried regardless of what I put in the where clause - what did I do wrong?

Had to step away from it for a minute, came back to figuring it had to be the contraints. I had implemented emailaddress like '[a-m]%' and emailaddress like '[n-z]%', and the optimizer just doesn't find those useful! They work as constraints, they just don't help the query plan. Changing to emailaddress < 'N' solved the problem. Not intuitive, but I guess not the end of the world either. But it's no fun when the live unplanned demo doesn't work!