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SQL Server Help: Using Cursors in Transact-SQL

What are cursors and how are they useful?

It is useful to know how to use Cursors in SQL Server's Transact SQL, as they can sometimes be used to perform SQL queries that would be very difficult to write without them. Unfortunately Cursors can be quite resource intensive, so they should only be used if there is no alternative way of writing a query.

The most useful feature of Cursors is the ability for them to process a set of database rows and perform some operation on each of the rows in turn. For example, the SQL query below uses a cursor to return a results set for each employee's orders:

USE Northwind
GO

DECLARE @Counter INT
DECLARE @EmployeeID INT

DECLARE Employees_Cursor CURSOR FOR
SELECT EmployeeID FROM Employees
OPEN Employees_Cursor
FETCH NEXT FROM Employees_Cursor into @EmployeeID
WHILE @@FETCH_STATUS = 0
BEGIN

SELECT * FROM Orders WHERE EmployeeID = @EmployeeID


FETCH NEXT FROM Employees_Cursor into @EmployeeID
END
CLOSE Employees_Cursor
DEALLOCATE Employees_Cursor

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