那就这样做
If e.DataCol.Name = "接单日期" Then
If e.DataRow.IsNull("接单日期") Then
e.DataRow("工单编号") = Nothing
Else
Dim d As Date = e.DataRow("接单日期")
Dim y As Integer = d.Year
Dim m As Integer = d.Month
Dim fd As Date = New Date(y,m,1) '获得该月的第一天
Dim ld As Date = fd.AddYears(1)
Dim bh As String = Format(d,"yy") '生成编号的前6位,4位年,2位月.
If e.DataRow("工单编号").StartsWith(bh) = False '如果编号的前4位不符
Dim max As String
Dim idx As Integer
max = e.DataTable.Compute("Max(工单编号)","接单日期 >= #" & fd & "# And 接单日期 < #" & ld & "# And [_Identify] <> " & e.DataRow("_Identify")) '取得该月的最大编号
If max > "" Then '如果存在最大编号
idx = CInt(max.Substring(bh.length)) + 1 '获得最大编号的后三位顺序号,并加1
Else
idx = 1 '否则顺序号等于1
End If
e.DataRow("工单编号") = bh & Format(idx,"0000")
e.DataRow("加上月份的编号") = Format(d,"yyMM") & Format(idx,"0000")
End If
End If
End If