Jack,

Getting following error

Msg 8154, Level 16, State 1, Line 1

The table 'Orders' is ambiguous.

here is the script

CREATE TABLE ORDERS(OrderNo int, OrderDate datetime, Cost int, PreviousCost int, NewCost int)...

Here is my intial table looks like

OrderNo OrderDate Cost PreviousCost NewCost

1 ...

Ignore the previous question. Here is what I need.

If the orderno exists in immediate previous month, then update the previousCost column with cost other wise update the newcost column with...