sort out

I have SQL tables column named "who" contains many names I want to sort out
all the name that is the same for exampel kolumnet have name 
martin 
sara 
martin 
sara 
I want the result is just showing 
martin 
sara 
thanks

 Sub itime()
        Using con As New SqlConnection(My.Settings.bbbaConnectionString)
            Dim command As New SqlCommand

            con.Open()


            Command = New SqlCommand( _
                         "SELECT vem FROM mam", con)
            Dim dr As SqlDataReader = Command.ExecuteReader()

            While (dr.Read())
                väljnamComboBox.Items.Add(dr.GetString(0))
            End While
        End Using
    End Sub