Erik Darling continues a series on understanding plains. First up is aggregate operators:
Aggregates can be useful for all sorts of things in a query plan, and can show up in many different forms.
It would be tough to cover all of them in a single post, but what I’d like to do is help all you nice folks out there understand some of their finer points.
Anyone who tells you there are only three types of joins in SQL Server isn’t your friend.
Okay, maybe that’s harsh. Maybe they’re just getting you prepared for the bonne promenade through all the many different faces a join can wear in your query plans.
Maybe they have a great explanation for Grace Hash Joins in their back pocket that they’re waiting to throw in your face like a bunch of glitter.
Do read both.