TSQL Cursor Infinite Loop without TOP xxx in SELECT Statement - tsql

Question

I have a curious problem with an infinite loop in a TSQL cursor. The cursor loops infinitely when I do not add TOP 300 to the defining select statement of the cursor. The following is an example of the code: Any assistance to this issue is much appreciated.
DECLARE #Done BIT
SET #Done = 0
DECLARE cursOut CURSOR LOCAL FAST_FORWARD
FOR
SELECT
--TOP 300
FirstName FirstName
,LastName LastName
,MiddleName MiddleName
,Email Email
,Address1 Address1
,Address2 Address2
,City City
,[State] [State]
FROM StagedUsers
OPEN cursOut;
WHILE (#Done = 0)
BEGIN
--Fetch next row
FETCH NEXT
FROM cursOut
INTO ,#v_FirstName
,#v_LastName
,#v_MiddleName
,#v_Email
,#v_Address1
,#v_Address2
,#v_City
,#v_State
IF (##FETCH_STATUS <> 0)
BEGIN
SET #Done = 1
BREAK
END
--if #batch = 0
BEGIN TRANSACTION
--process statements
--updates or insert statements
--Commit transaction
COMMIT TRANSACTION
--End While
END
--CleanUp:
CLOSE cursOut
DEALLOCATE cursOut
Thanks,
Renegrin

Answer 1

First I think you do not need transaction here, I presume it is only one statement executed, so remove transaction from code.
Second do it without #done flag, it is confusing (it is probably not problem here).
DECLARE #v_FirstName VARCHAR(500),#v_LastName VARCHAR(500),#v_MiddleName VARCHAR(500),#v_Email VARCHAR(500),#v_Address1 VARCHAR(500),#v_Address2 VARCHAR(500),#v_City VARCHAR(500),#v_State VARCHAR(500)
DECLARE cursOut CURSOR FAST_FORWARD FOR
SELECT FirstName FirstName,LastName LastName,MiddleName MiddleName,Email Email,Address1 Address1,Address2 Address2,City City,[State] [State]
FROM StagedUsers
OPEN cursOut;
FETCH NEXT FROM cursOut INTO #v_FirstName,#v_LastName,#v_MiddleName,#v_Email,#v_Address1,#v_Address2,#v_City,#v_State
declare #i int = 1
WHILE ##FETCH_STATUS = 0
BEGIN
print cast(#i as varchar(10))
--> statement here
FETCH NEXT FROM cursOut INTO #v_FirstName,#v_LastName,#v_MiddleName,#v_Email,#v_Address1,#v_Address2,#v_City,#v_State
set #i = #i + 1
END
CLOSE cursOut
DEALLOCATE cursOut
Do you want to update current row where cursor point? If so, there is way to do it.
Is there any indexes on table? Can you post an update query?