I think if we use Inner Join can solve the matter, as I just used and it works ok
Dim StrSql As String
StrSql = "UPDATE (SELECT Sales.Product, Sales.SQty, Sales.SRunTot,sales.sinv,salesm.sdate "
StrSql = StrSql & "FROM Sales inner join salesm on sales.sinv=salesm.sinv ORDER BY...