How to organize infinite while loop in SQL Server? - sql

Question

I want to use infinite WHILE loop in SQL Server 2005 and use BREAK keyword to exit from it on certain condition.
while true does not work, so I have to use while 1=1.
Is there a better way to organize infinite loop ?
I know that I can use goto, but while 1=1 begin ... end looks better structurally.

Answer 1

In addition to the WHILE 1 = 1 as the other answers suggest, I often add a "timeout" to my SQL "infintie" loops, as in the following example:
DECLARE #startTime datetime2(0) = GETDATE();
-- This will loop until BREAK is called, or until a timeout of 45 seconds.
WHILE (GETDATE() < DATEADD(SECOND, 45, #startTime))
BEGIN
-- Logic goes here: The loop can be broken with the BREAK command.
-- Throttle the loop for 2 seconds.
WAITFOR DELAY '00:00:02';
END
I found the above technique useful within a stored procedure that gets called from a long polling AJAX backend. Having the loop on the database-side frees the application from having to constantly hit the database to check for fresh data.

Answer 2

Using While 1 = 1 with a Break statement is the way to do it. There is no constant in T-SQL for TRUE or FALSE.

Answer 3

If you really have to use an infinite loop than using while 1=1 is the way I'd do it.
The question here is, isn't there some other way to avoid an infinite loop? These things just tend to go wrong ;)

Answer 4

you could use the snippet below to kick a sp after soem condition are rised. I assume that you ahev some sort of CurrentJobStatus table where all the jobs/sp keeps their status...
-- *** reload data on N Support.usp_OverrideMode with checks on Status
/* run
Support.usp_OverrideMode.Number1.sql
and
Support.usp_OverrideMode.Number2.sql
*/
DECLARE #FileNameSet TABLE (FileName VARCHAR(255));
INSERT INTO #FileNameSet
VALUES ('%SomeID1%');
INSERT INTO #FileNameSet
VALUES ('%SomeID2%');
DECLARE #BatchRunID INT;
DECLARE #CounterSuccess INT = 0;
DECLARE #CounterError INT = 0;
-- Loop
WHILE WHILE (#CounterError = 0 AND #CounterSuccess < (select COUNT(1) c from #FileNameSet) )
BEGIN
DECLARE #CurrenstStatus VARCHAR(255)
SELECT #CurrenstStatus = CAST(GETDATE() AS VARCHAR)
-- Logic goes here: The loop can be broken with the BREAK command.
SELECT #CounterSuccess = COUNT(1)
FROM dbo.CurrentJobStatus t
INNER JOIN #FileNameSet fns
ON (t.FileName LIKE fns.FileName)
WHERE LoadStatus = 'Completed Successfully'
SELECT #CounterError = COUNT(1)
FROM dbo.CurrentJobStatus t
INNER JOIN #FileNameSet fns
ON (t.FileName LIKE fns.FileName)
WHERE LoadStatus = 'Completed with Error(s)'
-- Throttle the loop for 3 seconds.
WAITFOR DELAY '00:00:03';
select #CurrenstStatus = #CurrenstStatus +char(9)+ '#CounterSuccess ' + CAST(#CounterSuccess AS VARCHAR(11))
+ char(9)+ 'CounterError ' + CAST(#CounterError AS VARCHAR(11))
RAISERROR (
'Looping... # %s'
,0
,1
,#CurrenstStatus
)
WITH NOWAIT;
END
-- TODO add some codition on #CounterError value
/* run
Support.usp_OverrideMode.WhenAllSuceed.sql
*/
Note the code is flexibile you can add as many condition checks on the #FileNameSet table var
Mario