this is typically how i do it.

1. do a full backup, just in case.

2. SELECT the rows that in theory, should be affected...we might get a specific row count out of this, which we want our update to match:

SELECT *

FROM dbo.tabletoupdate MyTargetTable

LEFT OUTER JOIN ExcelDataSource...sheet1$ MyExcel

ON MyTargetTable.ItemID = MyExcel.ItemID

WHERE MyTargetTable.WHAREHOUSE <> MyExcel.WHAREHOUSE

3. create an explicit transaction with teh update statement , and let it run:

SET XACT_ABORT ON

BEGIN TRAN

--much more explicit, only change rows that are different

UPDATE MyTargetTable

SET WHAREHOUSE = MyExcel.WHAREHOUSE

--SELECT *

FROM dbo.tabletoupdate MyTargetTable

LEFT OUTER JOIN ExcelDataSource...sheet1$ MyExcel

ON MyTargetTable.ItemID = MyExcel.ItemID

WHERE MyTargetTable.WHAREHOUSE <> MyExcel.WHAREHOUSE

--ROLLBACK TRAN

--COMMIT TRAN

4. IMPORTANT Note the above has both COMMIT TRAN and ROLLBACK TRAN COMMENTED OUT! the table's going to be locked untill you are done reviewing and you either commit or rollback!

5. Review the data in general, mae sure it looks good.

SELECT *

FROM dbo.tabletoupdate MyTargetTable

LEFT OUTER JOIN ExcelDataSource...sheet1$ MyExcel

ON MyTargetTable.ItemID = MyExcel.ItemID

6. lets go ahead and commit, if it's good.

COMMIT TRAN

7. IF it was bad, just ROLLBACK the transaction and start fresh.

ROLLBACK TRAN