Applies To: SQL Server 2014, SQL Server 2016 Preview
Topic Status: Some information in this topic is preview and subject to change in future releases. Preview information describes new features or changes to existing features in Microsoft SQL Server 2016 Community Technology Preview 2 (CTP2).
Removes a cursor reference. When the last cursor reference is deallocated, the data structures comprising the cursor are released by Microsoft SQL Server.
Applies to: SQL Server (SQL Server 2008 through current version), Azure SQL Database.
Statements that operate on cursors use either a cursor name or a cursor variable to refer to the cursor. DEALLOCATE removes the association between a cursor and the cursor name or cursor variable. If a name or variable is the last one referencing the cursor, the cursor is deallocated and any resources used by the cursor are freed. Scroll locks used to protect the isolation of fetches are freed at DEALLOCATE. Transaction locks used to protect updates, including positioned updates made through the cursor, are held until the end of the transaction.
The DECLARE CURSOR statement allocates and associates a cursor with a cursor name.
DECLARE abc SCROLL CURSOR FOR SELECT * FROM Person.Person;
After a cursor name is associated with a cursor, the name cannot be used for another cursor of the same scope (GLOBAL or LOCAL) until this cursor has been deallocated.
A cursor variable is associated with a cursor using one of two methods:
By name using a SET statement that sets a cursor to a cursor variable.
DECLARE @MyCrsrRef CURSOR; SET @MyCrsrRef = abc;
A cursor can also be created and associated with a variable without having a cursor name defined.
DECLARE @MyCursor CURSOR; SET @MyCursor = CURSOR LOCAL SCROLL FOR SELECT * FROM Person.Person;
A DEALLOCATE @cursor_variable_name statement removes only the reference of the named variable to the cursor. The variable is not deallocated until it goes out of scope at the end of the batch, stored procedure, or trigger. After a DEALLOCATE @cursor_variable_name statement, the variable can be associated with another cursor using the SET statement.
USE AdventureWorks2012; GO DECLARE @MyCursor CURSOR; SET @MyCursor = CURSOR LOCAL SCROLL FOR SELECT * FROM Sales.SalesPerson; DEALLOCATE @MyCursor; SET @MyCursor = CURSOR LOCAL SCROLL FOR SELECT * FROM Sales.SalesTerritory; GO
A cursor variable does not have to be explicitly deallocated. The variable is implicitly deallocated when it goes out of scope.
The following script shows how cursors persist until the last name or until the variable referencing them has been deallocated.
USE AdventureWorks2012; GO -- Create and open a global named cursor that -- is visible outside the batch. DECLARE abc CURSOR GLOBAL SCROLL FOR SELECT * FROM Sales.SalesPerson; OPEN abc; GO -- Reference the named cursor with a cursor variable. DECLARE @MyCrsrRef1 CURSOR; SET @MyCrsrRef1 = abc; -- Now deallocate the cursor reference. DEALLOCATE @MyCrsrRef1; -- Cursor abc still exists. FETCH NEXT FROM abc; GO -- Reference the named cursor again. DECLARE @MyCrsrRef2 CURSOR; SET @MyCrsrRef2 = abc; -- Now deallocate cursor name abc. DEALLOCATE abc; -- Cursor still exists, referenced by @MyCrsrRef2. FETCH NEXT FROM @MyCrsrRef2; -- Cursor finally is deallocated when last referencing -- variable goes out of scope at the end of the batch. GO -- Create an unnamed cursor. DECLARE @MyCursor CURSOR; SET @MyCursor = CURSOR LOCAL SCROLL FOR SELECT * FROM Sales.SalesTerritory; -- The following statement deallocates the cursor -- because no other variables reference it. DEALLOCATE @MyCursor; GO