怎么找出Excel一列中相同的值

如何找出Excel一列中相同的值
如题

------解决方案--------------------
上面错了 
这个
Private Sub CommandButton1_Click()

Dim j As Integer
Dim m As Integer
Dim i As Integer

j = 1
m = 2

For i = 1 To 20

For j = 1 To 20

If Sheet1.Cells(i, 3).Text = Sheet1.Cells(j, 3).Text Then
 
Cells(j, 3).Interior.ColorIndex = m + 1
Cells(i, 3).Interior.ColorIndex = m + 1


End If
Next j
 

If Sheet1.Cells(i, 3).Text = "" Then
GoTo mex
End If

m = m + 1

Next i
mex:
End Sub