DECLARE CURSOR (Transact-SQL)
Applies to:
SQL Server
Azure SQL Database
Azure SQL Managed Instance
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 ISO standard and a syntax using a set of Transact-SQL extensions.
Transact-SQL syntax conventions
Syntax
ISO 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 ] ] ]
[ ; ]
Note
To view Transact-SQL syntax for SQL Server 2014 (12.x) and earlier versions, see Previous versions documentation.
Arguments
cursor_name
The name of the Transact-SQL server cursor defined. cursor_name must conform to the rules for 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, base table modifications aren't reflected in the data returned by fetches made to this cursor, and this cursor doesn't allow modifications. When ISO 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
isn't specified in an ISO DECLARE CURSOR
, NEXT
is the only fetch option supported. SCROLL
can't be specified if FAST_FORWARD
is also specified. If SCROLL
isn't specified, then only the fetch option NEXT
is available, and the cursor becomes FORWARD_ONLY
.
select_statement
A standard SELECT
statement that defines the result set of the cursor. The keywords FOR BROWSE
, and INTO
aren't 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.
READ_ONLY
Prevents updates made through this cursor. The cursor can't 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.
cursor_name
The name of the Transact-SQL server cursor defined. cursor_name must conform to the rules for 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 passes 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.
FORWARD_ONLY
Specifies that the cursor can only move forward and be scrolled from the first to the last row. FETCH NEXT
is the only supported fetch option. All insert, update, and delete statements made by the current user (or committed by other users) that affect rows in the result set, are visible as the rows are fetched. Because the cursor can't be scrolled backward, however, changes made to rows in the database after the row was fetched aren't visible through the cursor. Forward-only cursors are dynamic by default, meaning that all changes are detected as the current row is processed. This provides faster cursor opening and enables the result set to display updates made to the underlying tables. While forward-only cursors don't support backward scrolling, applications can return to the beginning of the result set by closing and reopening the cursor.
If FORWARD_ONLY
is specified without the STATIC
, KEYSET
, or DYNAMIC
keywords, the cursor operates as a dynamic cursor. When FORWARD_ONLY
or SCROLL
aren't 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.
STATIC
Specifies that the cursor always displays the result set as it was when the cursor was first opened, and 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 inserts, updates, and deletes made to base tables aren't reflected in the data returned by fetches made to this cursor, and this cursor doesn't detect changes made to the membership, order, or values of the result set after the cursor is opened. Static cursors might detect their own updates, deletes, and inserts, although they aren't required to do so.
For example, suppose a static cursor fetches a row, and another application then updates that row. If the application refetches the row from the static cursor, the values it sees are unchanged, despite the changes made by the other application. All types of scrolling are supported.
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. This cursor provides functionality between a static and a dynamic cursor in its ability to detect changes. Like a static cursor, it doesn't always detect changes to the membership and order of the result set. Like a dynamic cursor, it does detect changes to the values of rows in the result set.
Keyset-driven cursors are controlled by a set of unique identifiers (keys) known as the keyset. The keys are built from a set of columns that uniquely identify the rows in the result set. The keyset is the set of key values from all the rows returned by the query statement. With keyset-driven cursors, a key is built and saved for each row in the cursor and stored either on the client workstation or on the server. When you access each row, the stored key is used to fetch the current data values from the data source. In a keyset-driven cursor, result set membership is frozen when the keyset is fully populated. Thereafter, additions or updates that affect membership aren't a part of the result set until it reopens.
Changes to data values (made either by the keyset owner or other processes) are visible as the user scrolls through the result set:
If a row is deleted, an attempt to fetch the row returns an
@@FETCH_STATUS
of-2
because the deleted row appears as a gap in the result set. The key for the row exists in the keyset, but the row no longer exists in the result set.Inserts made outside the cursor (by other processes) are visible only if the cursor is closed and reopened. Inserts made from inside the cursor are visible at the end of the result set.
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 isn't 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 theWHERE CURRENT OF
clause.
Note
If the query references at least one table without a unique index, the keyset cursor is converted to a static cursor.
DYNAMIC
Defines a cursor that reflects all data changes made to the rows in its result set as you scroll around the cursor and fetch a new record, regardless of whether the changes occur from inside the cursor or by other users outside the cursor. Therefore all insert, update, and delete statements made by all users are visible through the cursor. The data values, order, and membership of the rows can change on each fetch. The ABSOLUTE
fetch option isn't supported with dynamic cursors. Updates made outside the cursor aren't visible until they're committed (unless the cursor transaction isolation level is set to UNCOMMITTED
).
For example, suppose a dynamic cursor fetches two rows, and another application then updates one of those rows and deletes the other. If the dynamic cursor then fetches those rows, it doesn't find the deleted row, but it displays the new values for the updated row.
FAST_FORWARD
Specifies a FORWARD_ONLY
, READ_ONLY
cursor with performance optimizations enabled. FAST_FORWARD
can't be specified if SCROLL
or FOR_UPDATE
is also specified. This type of cursor doesn't allow data modifications from inside the cursor.
Note
Both FAST_FORWARD
and FORWARD_ONLY
can be used in the same DECLARE CURSOR
statement.
READ_ONLY
Prevents updates made through this cursor. The cursor can't 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. SQL Server locks the rows as they are read into the cursor to ensure their availability for later modifications. SCROLL_LOCKS
can't be specified if FAST_FORWARD
or STATIC
is also specified.
OPTIMISTIC
Specifies that positioned updates or deletes made through the cursor don't succeed, if the row was updated since it was read into the cursor. SQL Server doesn't lock rows as they're 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
can't be specified if FAST_FORWARD
is also specified.
If STATIC
is specified along with the OPTIMISTIC
cursor argument, the combination of the two are implicitly converted to the equivalent of the combination of using STATIC
and READ_ONLY
arguments, or the STATIC
and FORWARD_ONLY
arguments.
TYPE_WARNING
Specifies that a warning message is sent to the client when the cursor is implicitly converted from the requested type to another.
No warning is sent to the client when the combination of OPTIMISTIC
and STATIC
cursor arguments are used, and the cursor is implicitly converted to the equivalent of a STATIC READ_ONLY
or STATIC FORWARD_ONLY
cursor. The conversion to READ_ONLY
turns into a FAST_FORWARD
and READ_ONLY
cursor from a clients' perspective.
select_statement
A standard SELECT
statement that defines the result set of the cursor. The keywords COMPUTE
, COMPUTE BY
, FOR BROWSE
, and INTO
aren't allowed within select_statement of a cursor declaration.
Note
You can use a query hint within a cursor declaration. However, if you also use the FOR UPDATE OF
clause, specify OPTION (<query_hint>)
after FOR UPDATE OF
.
SQL Server implicitly converts the cursor to another type if clauses in select_statement conflict with the functionality of the requested cursor type.
FOR 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 ISO 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 or ADO.
You can't mix the two forms. If you specify the SCROLL
or INSENSITIVE
keywords before the CURSOR
keyword, you can't 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 can't specify SCROLL
or INSENSITIVE
before the CURSOR
keyword.
If a DECLARE CURSOR
using Transact-SQL syntax doesn't specify READ_ONLY
, OPTIMISTIC
, or SCROLL_LOCKS
, the default is as follows:
If the
SELECT
statement doesn't support updates (insufficient permissions, accessing remote tables that don't support updates, and so on), the cursor isREAD_ONLY
.STATIC
andFAST_FORWARD
cursors default toREAD_ONLY
.DYNAMIC
andKEYSET
cursors default toOPTIMISTIC
.
Cursor names can only be referenced by other Transact-SQL statements. They can't be referenced by database API functions. For example, after declaring a cursor, the cursor name can't be referenced from OLE DB, ODBC, or ADO functions or methods. The cursor rows can't be fetched using the fetch functions or methods of the APIs; the rows can only be fetched by Transact-SQL FETCH
statements.
After a cursor is declared, these system stored procedures can be used to determine the characteristics of the cursor.
System stored procedures | Description |
---|---|
sp_cursor_list | Returns a list of cursors currently visible on the connection and their attributes. |
sp_describe_cursor | Describes the attributes of a cursor, such as whether it's a forward-only or scrolling cursor. |
sp_describe_cursor_columns | Describes the attributes of the columns in the cursor result set. |
sp_describe_cursor_tables | Describes the base tables accessed by the cursor. |
Variables might be used as part of the select_statement that declares a cursor. Cursor variable values don't change after a cursor is declared.
Permissions
Permissions of DECLARE CURSOR
default to any user that has SELECT
permissions on the views, tables, and columns used in the cursor.
Limitations
You can't use cursors or triggers on a table with a clustered columnstore index. This restriction doesn't apply to nonclustered columnstore indexes. You can use cursors and triggers on a table with a nonclustered columnstore index.
Examples
A. Use basic cursor and syntax
The result set generated at the opening of this cursor includes all rows and all columns in the table. 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 isn't specified.
DECLARE vend_cursor CURSOR
FOR SELECT * FROM Purchasing.Vendor
OPEN vend_cursor
FETCH NEXT FROM vend_cursor;
B. Use nested cursors to produce report output
The following example shows how cursors can be nested to produce complex reports. The inner cursor is declared for each vendor.
SET NOCOUNT ON;
DECLARE @vendor_id INT, @vendor_name NVARCHAR(50),
@message VARCHAR(80), @product NVARCHAR(50);
PRINT '-------- Vendor Products Report --------';
DECLARE vendor_cursor CURSOR FOR
SELECT VendorID, Name
FROM Purchasing.Vendor
WHERE PreferredVendorStatus = 1
ORDER BY VendorID;
OPEN vendor_cursor
FETCH NEXT FROM vendor_cursor
INTO @vendor_id, @vendor_name
WHILE @@FETCH_STATUS = 0
BEGIN
PRINT ' '
SELECT @message = '----- Products From Vendor: ' +
@vendor_name
PRINT @message
-- Declare an inner cursor based
-- on vendor_id from the outer cursor.
DECLARE product_cursor CURSOR FOR
SELECT v.Name
FROM Purchasing.ProductVendor pv, Production.Product v
WHERE pv.ProductID = v.ProductID AND
pv.VendorID = @vendor_id -- Variable value from the outer cursor
OPEN product_cursor
FETCH NEXT FROM product_cursor INTO @product
IF @@FETCH_STATUS <> 0
PRINT ' <<None>>'
WHILE @@FETCH_STATUS = 0
BEGIN
SELECT @message = ' ' + @product
PRINT @message
FETCH NEXT FROM product_cursor INTO @product
END
CLOSE product_cursor
DEALLOCATE product_cursor
-- Get the next vendor.
FETCH NEXT FROM vendor_cursor
INTO @vendor_id, @vendor_name
END
CLOSE vendor_cursor;
DEALLOCATE vendor_cursor;