主题：请教如何避免如下错误

 For Each a1 As String In mxkm

                        If filter = "" Then

                            filter = "dttzflmxb33 like '" & a1 & "*'"

                        Else

                            filter = filter & " or dttzflmxb33 like '" & a1 & "*'"

                        End If

jfje = DataTables("dttzflmxb").Compute("sum(dttzflmxb6)"," dttzflmxb33 is not null" & " and (" & filter & ")" )