What is common table expression?

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SQL-Server

I have begun reading about Common table expression and cannot think of a use case where I would need to use them. They would seem to be redundant as the same can be done with derived tables. Is there something I am missing or not understanding well? Can someone give me a simple example of limitations with regular select, derived or temp table queries to make the case of CTE? Any simple examples would be highly appreciated.

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I have begun reading about Common table expression and cannot think of a use case where I would need to use them. They would seem to be redundant as the same can be done with derived tables. Is there something I am missing or not understanding well? Can someone give me a simple example of limitations with regular select, derived or temp table queries to make the case of CTE? Any simple examples would be highly appreciated.