Cursors in SQL Server

                                                         

First thing first. Usage of Cursors is not encouraged in SQL Server as they are slow. You may go with WHILE loop if you need to iterate through a recordset.Cursor is a database object to retrieve data from a result set one row at a time, instead of the T-SQL commands that operate on all the rows in the result set at one time.So this is a row by row operation instead of a set based operation.


SQL Server Cursor Components: Cursors include following components:

1) DECLARE statements - Declare variables used in the code block.

2) SET\SELECT statements - Initialize the variables to a specific value.

3) DECLARE CURSOR statement - Populate the cursor with values that will be evaluated.

4) OPEN statement - Open the cursor to begin data processing.

5) FETCH NEXT statements - Assign the specific values from the cursor to the variables

NOTE - This logic is used for the initial population before the WHILE statement and then again during each loop in the process as a portion of the WHILE statement.

WHILE statement - Condition to begin and continue data processing.

BEGIN...END statement - Start and end of the code block.

CLOSE statement - Releases the current data and associated locks, but permits the cursor to be re-opened

DEALLOCATE statement - Destroys the cursor
Below is an example of a static cursor.
DECLARE @Id int
DECLARE @name varchar(50)
DECLARE @salary int
DECLARE cur_emp CURSOR STATIC FOR
SELECT EmpID,EmpName,Salary from ContractEmployee
OPEN cur_emp
FETCH NEXT FROM cur_emp INTO @Id,@name,@salary
--FETCH ABSOLUTE 3 FROM cur_emp INTO @Id,@name,@salary
WHILE @@Fetch_status = 0
BEGIN
PRINT 'ID : '+ convert(varchar(20),@Id)+', Name : '+@name+ ', Salary : '+convert(varchar(20),@salary)
--FETCH RELATIVE 3 FROM cur_emp INTO @Id,@name,@salary
FETCH NEXT FROM cur_emp INTO @Id,@name,@salary
END
CLOSE cur_emp
DEALLOCATE cur_emp


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