SQLServer Subqueries

Subquery in FROM clause

A subquery in a FROM clause acts similarly to a temporary table that is generated during the execution of a query and lost afterwards.

SELECT Managers.Id, Employees.Salary
FROM (
 SELECT Id
 FROM Employees
 WHERE ManagerId IS NULL
) AS Managers
JOIN Employees ON Managers.Id = Employees.Id

Subquery in SELECT clause

SELECT
 Id,
 FName,
 LName,
 (SELECT COUNT(*) FROM Cars WHERE Cars.CustomerId = Customers.Id) AS NumberOfCars
FROM Customers

Subquery in WHERE clause

Use a subquery to filter the result set. For example this will return all employees with a salary equal to the highest
paid employee.

SELECT *
FROM Employees
WHERE Salary = (SELECT MAX(Salary) FROM Employees)

Conclusion

In this page (written and validated by A. Gawali) you learned about SQLServer Subqueries . What's Next? If you are interested in completing SQLServer tutorial, your next topic will be learning about: SQLServer Execution blocks.

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