Apply Operator and CTE

Apply Operator and CTE

The APPLY operator and Common Table Expressions (CTE) are two powerful features of SQL Server 2008 that can greatly enhance the functionality of your queries.

The APPLY operator allows you to invoke a table-valued function for each row returned by a preceding table expression. This can be particularly useful when you need to perform a join-like operation between a table and a function that returns a set of rows. There are two types of APPLY operators: CROSS APPLY and OUTER APPLY. CROSS APPLY returns only the rows for which the function returns a non-empty result set, while OUTER APPLY returns all the rows from the preceding table expression, and for those rows for which the function returns an empty result set, it returns NULL values.

CTEs allow you to define a temporary result set that can be used within a query. The CTE is defined using a WITH clause, followed by a SELECT statement that defines the result set. You can then reference the CTE in subsequent SELECT, INSERT, UPDATE, or DELETE statements. CTEs are particularly useful when you need to perform complex queries that involve multiple subqueries, as they allow you to break down the problem into smaller, more manageable pieces. Overall, the APPLY operator and CTEs are powerful features of SQL Server 2008 that can help you write more efficient and readable queries.

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