SQL服务器中的游标？ [英] Cursor in SQL server?

问题描述

朋友们，





--OPEN CURSOR：



OPEN @getid



来自游标的FETCH行



FETCH NEXT





来自@getid INTO @id



WHILE @@ FETCH_STATUS



BEGIN



PRINT @id



FETCH NEXT



来自@getid INTO @id



结束



--CLOSE CURSOR



关闭@getid





- -DE-ALLOCATED CURSOR



DE-ALLOCATED @getid



i有点疑问，而@ @fetch_status

为什么我们在那里使用全局变量？任何一个澄清我的怀疑？

hi friends,


--OPEN CURSOR:

OPEN @getid

FETCH ROW FROM THE CURSOR

FETCH NEXT


FROM @getid INTO @id

WHILE @@FETCH_STATUS

BEGIN

PRINT @id

FETCH NEXT

FROM @getid INTO @id

END

--CLOSE CURSOR

CLOSE @getid


--DE-ALLOCATED CURSOR

DE-ALLOCATED @getid

i have doubt in while condition like while @@fetch_status
why we are using global variable there? any one clarify my doubt?

推荐答案

我不确定为什么它使用全局变量但这是我对这个主题的看法。



@@ FETCH_STATUS 对于连接上的所有游标都是全局的



http://msdn.microsoft.com/en-us/library/ms187308.aspx [ ^ ]



这意味着你必须要注意这种变量类型的行为。如果游标调用实现另一个游标的存储过程，则可能会产生问题，因为从存储过程返回时 @@ FETCH_STATUS 值无效。诀窍是确保在执行提取后立即评估提取的结果。



但通常情况下，你可以做一些事情方法。您可以使用 sys.dm_exec_cursors 管理功能检查任何给定游标的 fetch_status 。



请阅读此处了解有关此功能的更多详情。



http://msdn.microsoft.com/en-us/library/ms190346.aspx [ ^ ]

I''m not sure as to why it uses a global variable but here are my thoughts on the subject.

"@@FETCH_STATUS is global to all cursors on a connection"

http://msdn.microsoft.com/en-us/library/ms187308.aspx[^]

This means that you do have to be aware of the behaviour such variable type. You can create a problem if your cursor calls a stored procedure which implements another cursor as the @@FETCH_STATUS value will be invalid when returning from the stored procedure. The trick is to make sure you always evaluate the result of a fetch immediately after executing the fetch.

But as is often the way, you can do things a number of ways. You can check the fetch_status of any given cursor using the sys.dm_exec_cursors management function.

Read here for more details on this function.

http://msdn.microsoft.com/en-us/library/ms190346.aspx[^]

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