Common Table Expressions Are Not Tables

There's power in naming things. Supposedly some types of magic are even based on knowing the correct names for things. The name for the T-SQL clause¬†Common Table Expression (CTE) is actually pretty accurate. It's an expression that looks like a table and can be used in common across the entire query (at least I think that's what the common part refers to). But note, I didn't say it was a table. It's not. It's an expression. If you look at the T-SQL definition at the link, it refers to a "temporary" result set. Now, to a lot of people, that means table. But it isn't. Let's look at this in more detail. Here's a query that defines a simple CTE and then uses it to query the date in the…
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