crm 2011 - Delete system jobs using SQL

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IF EXISTS (SELECT name from sys.indexes
                  WHERE name = N'CRM_AsyncOperation_CleanupCompleted')
      DROP Index AsyncOperationBase.CRM_AsyncOperation_CleanupCompleted
GO
CREATE NONCLUSTERED INDEX CRM_AsyncOperation_CleanupCompleted
ON [dbo].[AsyncOperationBase] ([StatusCode],[StateCode],[OperationType])
GO

declare @DeleteRowCount int
Select @DeleteRowCount = 2000
declare @DeletedAsyncRowsTable table (AsyncOperationId uniqueidentifier not null primary key)
declare @continue int, @rowCount int
select @continue = 1
while (@continue = 1)
begin     
begin tran     
insert into @DeletedAsyncRowsTable(AsyncOperationId)
      Select top (@DeleteRowCount) AsyncOperationId from AsyncOperationBase
      where OperationType in (1, 9, 12, 25, 27, 10) --AND StateCode = 3 --AND StatusCode in (30, 32)    
       Select @rowCount = 0
      Select @rowCount = count(*) from @DeletedAsyncRowsTable
      select @continue = case when @rowCount <= 0 then 0 else 1 end     
        if (@continue = 1)        begin
            delete WorkflowLogBase from WorkflowLogBase W, @DeletedAsyncRowsTable d
            where W.AsyncOperationId = d.AsyncOperationId            
 delete BulkDeleteFailureBase From BulkDeleteFailureBase B, @DeletedAsyncRowsTable d
            where B.AsyncOperationId = d.AsyncOperationId
 delete WorkflowWaitSubscriptionBase from WorkflowWaitSubscriptionBase WS, @DeletedAsyncRowsTable d
 where WS.AsyncOperationId = d.AsyncOperationID
            delete AsyncOperationBase From AsyncOperationBase A, @DeletedAsyncRowsTable d
            where A.AsyncOperationId = d.AsyncOperationId            
            delete @DeletedAsyncRowsTable     
end      
commit
end
--Drop the Index on AsyncOperationBase
DROP INDEX AsyncOperationBase.CRM_AsyncOperation_CleanupCompleted






--Statuscode
--0    Waiting For Resources
--10    Waiting
--20    In Progress
--21    Pausing
--22    Canceling
--30    Succeeded
--31    Failed
--32    Canceled


--Statecode
--0    Ready
--1    Suspended
--2    Locked
--3    Completed

Refer >> http://support.microsoft.com/kb/968520