Thanks for this question! I recently re-learned this info, and the way I remembered it (I know it's probably a bad mnemonic but it works for me) is: "COUNT (ALL col) does not COUNT ALL" -meaning it excludes NULLs.
- webrunner
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A SQL query walks into a bar and sees two tables. He walks up to them and asks, "Can I join you?"
Ref.: http://tkyte.blogspot.com/2009/02/sql-joke.html