INSERT INTO MasterList(ComputerName, AuditID, IAV, [Date])
SELECT ComputerName, AuditID, IAV, [Date]
FROM Temp t
WHERE NOT EXISTS (SELECT 1
FROM MasterList ml
WHERE ml.ComputerName = t.ComputerName
AND ml.AuditID = t.AuditID
AND ml.IAV = t.IAV
AND ml.[Date] = t.[Date]);
If I may make a suggestion, don't give your fields a name that's the same as a reserved word. Call it "EntryDate" or something like that instead of just "Date".