common table expression - Use of With Clause in SQL Server -


How does with clause work in SQL Server? Does it really give me some performance boost or does it help in creating a more readable script?

When is it right to use it?

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Unless you use recursive capabilities, see a CTE simple inline.

It just saves you some typing.

The Optimizer is free to decide whether to re-evaluate it or not when it is being reused, and it decides to re-evaluate most cases: 

  with q (UUID) as select (select nude ()) Select all from the Q union * from q

You have two different New Eyes .

Note that other engines can behave differently. CTE .

PostgreSQL , Unlike SQL Server , CTE

Oracle is a special signal , Supports / * + MATERIALIZE * / , which tells the adapter that it should not be CTE or not.


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