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EXISTS - Testing Subquery Results in SQL Server
How To Test Subquery Results with the EXISTS Operator in SQL Server Transact-SQL?
✍: FYIcenter.com
EXISTS is a special operator used to test subquery results. EXISTS can be used in two ways:
EXISTS (SELECT ...) -- Returns TRUE if the specified subquery has one or more rows returned. NOT EXISTS (SELECT ...) -- Returns TRUE if the specified subquery no rows returned.
The following tutorial exercise shows you two examples of EXISTS operators. The sample database AdventureWorksLT provided by Microsoft is used.
USE AdventureWorksLT GO -- Number of customers with orders SELECT COUNT(*) FROM SalesLT.Customer c WHERE EXISTS ( SELECT * FROM SalesLT.SalesOrderHeader s WHERE s.CustomerID = c.CustomerID ) GO 32 -- Number of customers without orders SELECT COUNT(*) FROM SalesLT.Customer c WHERE NOT EXISTS ( SELECT * FROM SalesLT.SalesOrderHeader s WHERE s.CustomerID = c.CustomerID ) 408
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⇑ Boolean Values and Logical Operations in SQL Server Transact-SQL
2017-01-21, 1507🔥, 0💬
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