SQL: The value of NOT NULL

Most SQL resources teach only the language. It's hard to find blogs with useful advice, and even harder to find bloggers who back up their claims. Here is an excellent article:

"The NOT IN took over 5 times longer to execute and did thousands of times more reads."

That site has lots of interesting comparisons for various SQL queries.

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Here are some other useful links:

• Indexing
• SQL Myths