DECLARE CURSOR (T-SQL)

Defines the attributes of a Transact-SQL server cursor, such as its scrolling behavior and the query used to build the result set on which the cursor operates. DECLARE CURSOR accepts both a syntax based on the SQL-92 standard and a syntax using a set of Transact-SQL extensions.

SQL-92 Syntax

DECLARE cursor_name [INSENSITIVE] [SCROLL] CURSOR
FOR select_statement
[FOR {READ ONLY | UPDATE [OF column_name [,...n]]}]

Transact-SQL Extended Syntax

DECLARE cursor_name CURSOR
[LOCAL | GLOBAL]
[FORWARD_ONLY | SCROLL]
[STATIC | KEYSET | DYNAMIC | FAST_FORWARD]
[READ_ONLY | SCROLL_LOCKS | OPTIMISTIC]
[TYPE_WARNING]
FOR select_statement
[FOR UPDATE [OF column_name [,...n]]]

SQL-92 Arguments

cursor_name

Is the name of the Transact-SQL server cursor being defined. cursor_name must conform to the rules for identifiers. For more information, see Using Identifiers.

INSENSITIVE

Defines a cursor that makes a temporary copy of the data to be used by the cursor. All requests to the cursor are answered from this temporary table in tempdb; therefore, modifications made to base tables are not reflected in the data returned by fetches made to this cursor, and this cursor does not allow modifications. When SQL-92 syntax is used, if INSENSITIVE is omitted, committed deletes and updates made to the underlying tables (by any user) are reflected in subsequent fetches.

SCROLL

Specifies that all fetch options (FIRST, LAST, PRIOR, NEXT, RELATIVE, ABSOLUTE) are available. If SCROLL is not specified in an SQL-92 DECLARE CURSOR, NEXT is the only fetch option supported. SCROLL cannot be specified if FAST_FORWARD is also specified.

select_statement

Is a standard SELECT statement that defines the result set of the cursor. The keywords COMPUTE, COMPUTE BY, FOR BROWSE, and INTO are not allowed within select_statement of a cursor declaration.

Microsoft® SQL Server™ implicitly converts the cursor to another type if clauses in select_statement conflict with the functionality of the requested cursor type. For more information, see Implicit Cursor Conversions.

READ ONLY

Prevents updates from being made through this cursor. The cursor cannot be referenced in a WHERE CURRENT OF clause in an UPDATE or DELETE statement. This option overrides the default capability of a cursor to be updated.

UPDATE [OF column_name [,...n]]

Defines updatable columns within the cursor. If OF column_name [,...n] is specified, only the columns listed allow modifications. If UPDATE is specified without a column list, all columns can be updated.

Transact-SQL Extended Arguments

cursor_name

Is the name of the Transact-SQL server cursor being defined. cursor_name must conform to the rules for identifiers. For more information, see Using Identifiers.

LOCAL

Specifies that the scope of the cursor is local to the batch, stored procedure, or trigger in which the cursor was created. The cursor name is only valid within this scope. The cursor can be referenced by local cursor variables in the batch, stored procedure, or trigger, or a stored procedure OUTPUT parameter. An OUTPUT parameter is used to pass the local cursor back to the calling batch, stored procedure, or trigger, which can assign the parameter to a cursor variable to reference the cursor after the stored procedure terminates. The cursor is implicitly deallocated when the batch, stored procedure, or trigger terminates, unless the cursor was passed back in an OUTPUT parameter. If it is passed back in an OUTPUT parameter, the cursor is deallocated when the last variable referencing it is deallocated or goes out of scope.

GLOBAL

Specifies that the scope of the cursor is global to the connection. The cursor name can be referenced in any stored procedure or batch executed by the connection. The cursor is only implicitly deallocated at disconnect.

Note If neither GLOBAL or LOCAL is specified, the default is controlled by the setting of the default to local cursor database option. In SQL Server version 7.0, this option defaults to FALSE to match earlier versions of SQL Server, in which all cursors were global. The default of this option may change in future versions of SQL Server. For more information, see Setting Database Options.

FORWARD_ONLY

Specifies that the cursor can only be scrolled from the first to the last row. FETCH NEXT is the only supported fetch option. If FORWARD_ONLY is specified without the STATIC, KEYSET, or DYNAMIC keywords, the cursor operates as a DYNAMIC cursor. When neither FORWARD_ONLY nor SCROLL is specified, FORWARD_ONLY is the default, unless the keywords STATIC, KEYSET, or DYNAMIC are specified. STATIC, KEYSET, and DYNAMIC cursors default to SCROLL. Unlike database APIs such as ODBC and ADO, FORWARD_ONLY is supported with STATIC, KEYSET, and DYNAMIC Transact-SQL cursors. FAST_FORWARD and FORWARD_ONLY are mutually exclusive, if one is specified the other cannot be specified.

STATIC

Defines a cursor that makes a temporary copy of the data to be used by the cursor. All requests to the cursor are answered from this temporary table in tempdb; therefore, modifications made to base tables are not reflected in the data returned by fetches made to this cursor, and this cursor does not allow modifications.

KEYSET

Specifies that the membership and order of rows in the cursor are fixed when the cursor is opened. The set of keys that uniquely identify the rows is built into a table in tempdb known as the keyset. Changes to nonkey values in the base tables, either made by the cursor owner or committed by other users, are visible as the owner scrolls around the cursor. Inserts made by other users are not visible (inserts cannot be made through a Transact-SQL server cursor). If a row is deleted, an attempt to fetch the row returns an @@FETCH_STATUS of -2. Updates of key values from outside the cursor resemble a delete of the old row followed by an insert of the new row. The row with the new values is not visible, and attempts to fetch the row with the old values return an @@FETCH_STATUS of -2. The new values are visible if the update is done through the cursor by specifying the WHERE CURRENT OF clause.

DYNAMIC

Defines a cursor that reflects all data changes made to the rows in its result set as you scroll around the cursor. The data values, order, and membership of the rows can change on each fetch. The ABSOLUTE fetch option is not supported with dynamic cursors.

FAST_FORWARD

Specifies a FORWARD_ONLY, READ_ONLY cursor with performance optimizations enabled. FAST_FORWARD cannot be specified if SCROLL or FOR_UPDATE is also specified. FAST_FORWARD and FORWARD_ONLY are mutually exclusive, if one is specified the other cannot be specified.

READ_ONLY

Prevents updates from being made through this cursor. The cursor cannot be referenced in a WHERE CURRENT OF clause in an UPDATE or DELETE statement. This option overrides the default capability of a cursor to be updated.

SCROLL_LOCKS

Specifies that positioned updates or deletes made through the cursor are guaranteed to succeed. Microsoft® SQL Server™ locks the rows as they are read into the cursor to ensure their availability for later modifications. SCROLL_LOCKS cannot be specified if FAST_FORWARD is also specified.

OPTIMISTIC

Specifies that positioned updates or deletes made through the cursor do not succeed if the row has been updated since it was read into the cursor. SQL Server does not lock rows as they are read into the cursor. It instead uses comparisons of timestamp column values, or a checksum value if the table has no timestamp column, to determine whether the row was modified after it was read into the cursor. If the row was modified, the attempted positioned update or delete fails. OPTIMISTIC cannot be specified if FAST_FORWARD is also specified.

TYPE_WARNING

Specifies that a warning message is sent to the client if the cursor is implicitly converted from the requested type to another.

select_statement

Is a standard SELECT statement that defines the result set of the cursor. The keywords COMPUTE, COMPUTE BY, FOR BROWSE, and INTO are not allowed within select_statement of a cursor declaration.

SQL Server implicitly converts the cursor to another type if clauses in select_statement conflict with the functionality of the requested cursor type. For more information, see Implicit Cursor Conversions.

UPDATE [OF column_name [,...n]]

Defines updatable columns within the cursor. If OF column_name [,...n] is supplied, only the columns listed allow modifications. If UPDATE is specified without a column list, all columns can be updated, unless the READ_ONLY concurrency option was specified.

Remarks

DECLARE CURSOR defines the attributes of a Transact-SQL server cursor, such as its scrolling behavior and the query used to build the result set on which the cursor operates. The OPEN statement populates the result set, and FETCH returns a row from the result set. The CLOSE statement releases the current result set associated with the cursor. The DEALLOCATE statement releases the resources used by the cursor.

The first form of the DECLARE CURSOR statement uses the SQL-92 syntax for declaring cursor behaviors. The second form of DECLARE CURSOR uses Transact-SQL extensions that allow you to define cursors using the same cursor types used in the database API cursor functions of ODBC, ADO, and DB-Library.

You cannot mix the two forms. If you specify the SCROLL or INSENSITIVE keywords before the CURSOR keyword, you cannot use any keywords between the CURSOR and FOR select_statement keywords. If you specify any keywords between the CURSOR and FOR select_statement keywords, you cannot specify SCROLL or INSENSITIVE before the CURSOR keyword.

If a DECLARE CURSOR using Transact-SQL syntax does not specify READ_ONLY, OPTIMISTIC, or SCROLL_LOCKS, the default is as follows:

• If the SELECT statement does not support updates (insufficient permissions, accessing remote tables that do not support updates, and so on), the cursor is READ_ONLY.
• STATIC and FAST_FORWARD cursors default to READ_ONLY.
• DYNAMIC, and KEYSET cursors default to OPTIMISTIC.

Cursor names can be referenced only by other Transact-SQL statements. They cannot be referenced by database API functions. For example, after declaring a cursor, the cursor name cannot be referenced from OLE DB, ODBC, ADO, or DB-Library functions or methods. The cursor rows cannot be fetched using the fetch functions or methods of the APIs; the rows can be fetched only by Transact-SQL FETCH statements.

After a cursor has been declared, these system stored procedures can be used to determine the characteristics of the cursor.

Permissions

DECLARE CURSOR permissions default to any user that has SELECT permissions on the views, tables, and columns used in the cursor.

Examples

A. Use simple cursor and syntax

The result set generated at the opening of this cursor includes all rows and all columns in the authors table of the pubs database. This cursor can be updated, and all updates and deletes are represented in fetches made against this cursor. FETCH NEXT is the only fetch available because the SCROLL option has not been specified.

DECLARE authors_cursor CURSOR

    FOR SELECT * FROM authors

OPEN authors_cursor

FETCH NEXT FROM authors_cursor

B. Use nested cursors to produce report output

This example shows how cursors can be nested to produce complex reports. The inner cursor is declared for each author.

SET NOCOUNT ON

DECLARE @au_id varchar(11), @au_fname varchar(20), @au_lname varchar(40),

    @message varchar(80), @title varchar(80)

PRINT "-------- Utah Authors report --------"

DECLARE authors_cursor CURSOR FOR

SELECT au_id, au_fname, au_lname

FROM authors

WHERE state = "UT"

ORDER BY au_id

OPEN authors_cursor

FETCH NEXT FROM authors_cursor

INTO @au_id, @au_fname, @au_lname

WHILE @@FETCH_STATUS = 0

BEGIN

    PRINT " "

    SELECT @message = "----- Books by Author: " +

        @au_fname + " " + @au_lname

    PRINT @message

    -- Declare an inner cursor based  

    -- on au_id from the outer cursor.

    DECLARE titles_cursor CURSOR FOR

    SELECT t.title

    FROM titleauthor ta, titles t

    WHERE ta.title_id = t.title_id AND

    ta.au_id = @au_id    -- Variable value from the outer cursor

    OPEN titles_cursor

    FETCH NEXT FROM titles_cursor INTO @title

    IF @@FETCH_STATUS <> 0

        PRINT "         <<No Books>>"    

    WHILE @@FETCH_STATUS = 0

    BEGIN

        SELECT @message = "         " + @title

        PRINT @message

        FETCH NEXT FROM titles_cursor INTO @title

    END

    CLOSE titles_cursor

    DEALLOCATE titles_cursor

    -- Get the next author.

    FETCH NEXT FROM authors_cursor

    INTO @au_id, @au_fname, @au_lname

END

CLOSE authors_cursor

DEALLOCATE authors_cursor

GO

-------- Utah Authors report --------

----- Books by Author: Anne Ringer

         The Gourmet Microwave

         Is Anger the Enemy?

----- Books by Author: Albert Ringer

         Is Anger the Enemy?

         Life Without Fear

See Also