SET NOCOUNT { ON | OFF }

Syntax

SET NOCOUNT { ON | OFF }

Stops the message that shows the count of the number of rows affected by a Transact-SQL statement or stored procedure
from being returned as part of the result set.

Remarks

When SET NOCOUNT is ON, the count is not returned. When SET NOCOUNT is OFF, the count is returned.

The @@ROWCOUNT function is updated even when SET NOCOUNT is ON.

SET NOCOUNT ON prevents the sending of DONE_IN_PROC messages to the client for each statement in a stored procedure. For stored procedures that contain several statements that do not return much actual data, or for procedures that contain Transact-SQL loops,
setting SET NOCOUNT to ON can provide a significant performance boost, because network traffic is greatly reduced.

The setting specified by SET NOCOUNT is in effect at execute or run time and not at parse time.

以sp_who为例做下解释：

SET NOCOUNT OFF
EXEC sp_who

SET NOCOUNT ON
EXEC sp_who

可以看出除了返回我们所想要的results的外，SET NOCOUNT OFF,还返回所影响的行数,SET NOCOUNT ON,则只返回SQL执行成功.

这样做的好处：

提高了SQL执行性能,优化项目。