Jeff, you've never steered me wrong in my years of SQL'ing. It'd be an honor to meet you in person some day. In the meantime, I'd LOVE to see a...

Is it possible that the LEFT JOIN is producing a different execution plan which just happens to be exposing some other unknown issue in your data? Perhaps a join to...

Hope these aren't real email addresses...

LOL @ "not to go 'All Celko' on you"!

I think you should. This individual is making your community a more abrasive, unfriendly place. All the all-stars have tried to rein him in and it has no effect whatsoever....

Wait, using "NOT EXISTS" is bad?

Yes, for the sake of this thread, it's safe to assume no overlaps. But good question. Thank you guys!

DREW = TOO SEXY

I'd guess that...
partition by ld.DatabasesInstanceUsers_SQN order by ld.DatabasesInstanceUsers_LDTS
...is not producing the same results each time you run it. you have a tie in there or something.

I always learn something here! Never fails.

^ but isn't that "non-sargable"?

This has to be one of the vaguest and most unclear questions I've ever seen on this site. But is this what you're getting at?

SELECT [mycrap]

Might be a good time to add a useful primary key to your table. 🙂

Safe bet it was the GROUP BY.

I woulda thought a straight INNER JOIN would be the easiest for the engine to optimize for. But good food for thought.