How do I save a record without duplicate values in ID

Private Sub cmdsave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdsave.Click
        If txtid.Text = "" Or txtname.Text = "" Or txtmn.Text = "" Or txtln.Text = "" Or cbogender.Text = "" Or cbosub.Text = "" Or cbopos.Text = "" Then
            MsgBox("Complete All Fields Needed", MsgBoxStyle.Information, "")
            txtid.Focus()
        ElseIf IsNumeric(txtid.Text) = False Then
            MsgBox("ID number should be numbers only")
        ElseIf sb = True Then
            mycmd.Connection = mycon
            mycmd.CommandText = "insert into `tbluseradmin`(`ID`,`Name`,`MiddleName`,`LastName`,`Gender`,`Subject`,`Position`)values('" & txtid.Text & "','" & txtname.Text & "','" & txtmn.Text & "','" & txtln.Text & "','" & cbogender.Text & "','" & cbosub.Text & "','" & cbopos.Text & "')"
            mycmd.ExecuteNonQuery()
            mycon.Close()
            My.Computer.FileSystem.CopyFile(ofd.FileName, Application.StartupPath & "\images\" & txtid.Text & ".jpg")
            MsgBox("Record Save", MsgBoxStyle.Information, "")
            Call connect()
            Call display()
            Call textboxlocked()
            Call buttonunlock()
            Call cmdlock()
            Call cmd2unlock()
        Else
            mycmd.Connection = mycon
            mycmd.CommandText = "update `tbluseradmin` set`ID`='" & txtid.Text & "',`Name`='" & txtname.Text & "',`MiddleName`='" & txtmn.Text & "',`LastName`='" & txtln.Text & "',`Gender`='" & cbogender.Text & "'where`ID`='" & idnum & "'"
            mycmd.ExecuteNonQuery()
            mycon.Close()
            My.Computer.FileSystem.CopyFile(ofd.FileName, Application.StartupPath & "\images\" & txtid.Text & ".jpg")
            MsgBox("Record Update", MsgBoxStyle.Information, "")
            Call connect()
            Call display()
            Call textboxlocked()
            Call buttonunlock()
            Call cmdlock()
            Call cmd2unlock()


        End If
    End Sub