SELECT *
FROM Table t
WHERE BuyDate > = DATEADD(mm,DATEDIFF(mm,0,GETDATE()),0)
AND BuyDate < DATEADD(mm,DATEDIFF(mm,0,GETDATE())+1,0)
AND NOT EXISTS (SELECT 1 FROM table WHERE CustomerID = t.CustomerID AND BuyDate < DATEADD(mm,DATEDIFF(mm,0,GETDATE()),0)
AND other conditions...)
AND other conditions....
------------------------------------------------------------------------------------------------------
SQL Server MVP
http://visakhm.blogspot.com/