How to prevent duplicate data in a combobox using database

[Royer12]

Hello, I have a database that I connect as follows

Public Class Frm2
Dim cnn As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source= data.accdb;Persist Security Info=False")


Private Sub Frm2_Load(sender As Object, e As EventArgs) Handles MyBase.Load

Dim sql As String = "SELECT Alumn.Id_school,Esc.school FROM Esc,Alumn"
Cmb_scuel.DataSource = loadded(sql)
Cmb_scuel.DisplayMember = "school" 'table Esc name
Cmb_scuel.ValueMember = "Id_school" 'table Alumn id

Private Function loadded(sql As String) As DataTable
Dim dt As New DataTable
Using cmd As New OleDbCommand(sql, cnn)
cnn.Open()
Dim adapter As New OleDbDataAdapter(cmd)
adapter.Fill(dt)
cnn.Close()
End Using
Return dt
End Function
End Sub
End Class

it turns out that when compiling, the same data is displayed in the combobox but they are repeated constantly.

just to clarify, I have 4 data and these four are repeated 5 times

that is 4x5 = 20 datas.

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