How am I going to display duplicate data in gridview by clicking a button?

See more:

VB

SQL-Server

Gridview

I want to display all the duplicate data in this gridview. But, i dont have any idea on how it works. What i have tried seem not working at all. Mind to share any ideas?

What I have tried:

Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

        Dim cn As String = 
        ConfigurationManager.ConnectionStrings("zzzzz").ConnectionString
        Using cs As New SqlConnection(cn)
        Using cmd As New SqlCommand("SELECT xxxxx, COUNT(*) FROM vvvvv GROUP BY xxxxx HAVING COUNT(*) > 1", cs)
                Using sda As New SqlDataAdapter(cmd)
                    Dim dt As New DataTable()
                    sda.Fill(dt)
                    rptTableUser3.DataSource = dt
                    rptTableUser3.DataBind()
                End Using
            End Using
        End Using

    End Sub