Cursors (Transact-SQL)

Cursors (Transact-SQL)

Microsoft SQL Server statements produce a complete result set, but there are times when the results are best processed one row at a time. Opening a cursor on a result set allows processing the result set one row at a time. You can assign a cursor to a variable or parameter with a cursor data type.

Cursor operations are supported on these statements:

CLOSE

CREATE PROCEDURE

DEALLOCATE

DECLARE CURSOR

DECLARE @local_variable

DELETE

FETCH

OPEN

UPDATE

SET

These system functions and system stored procedures also support cursors:

@@CURSOR_ROWS

CURSOR_STATUS

@@FETCH_STATUS

sp_cursor_list

sp_describe_cursor

sp_describe_cursor_columns

sp_describe_cursor_tables

See Also

Cursors

 

 

DECLARE CURSOR (Transact-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 ISO standard and a syntax using a set of Transact-SQL extensions.

 

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 ] ] ]  
[;]  

 

What is the use of a cursor in SQL Server?

Cursors are a mechanism to explicitly enumerate through the rows of a result set, rather than retrieving it as such.

However, while they may be more comfortable to use for programmers accustomed to writing While Not RS.EOF Do ..., they are typically a thing to be avoided within SQL Server stored procedures if at all possible -- if you can write a query without the use of cursors, you give the optimizer a much better chance to find a fast way to implement it.

In all honesty, I've never found a realistic use case for a cursor that couldn't be avoided, with the exception of a few administrative tasks such as looping over all indexes in the catalog and rebuilding them. I suppose they might have some uses in report generation or mail merges, but it's probably more efficient to do the cursor-like work in an application that talks to the database, letting the database engine do what it does best -- set manipulation.

 

作者:Chuck Lu    GitHub