Bỏ qua / bỏ qua các hàng trùng lặp khi chèn

INSERT dbo.DataValue(DateStamp, ItemId, Value)
SELECT DateStamp, ItemId, Value 
FROM dbo.tmp_holding_DataValue AS t
WHERE NOT EXISTS (SELECT 1 FROM dbo.DataValue AS d
WHERE DateStamp = t.DateStamp
AND ItemId = t.ItemId);