Joins are a thing you learn on Day 1 of T-SQL 101. But they are so much more involved than what you learned then. Logical v physical, Semi Joins, Lookup Joins, Redundant Joins, not to mention those times when you thought you specified one kind of join and the execution plan says it's doing something else.

Luckily, it's not magic - it's all very straightforward once you understand the different types of joins and how they work. This session will cover the different types of logical and physical joins - and even look at joins that don't exist at all.
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Presented by Rob Farley at SQLBits XVII