งง กับการ Insert ID ค่ะแนะนำด้วยค่ะ คือถ้า ID ซ้ำกันให้ บอกถ้าไม่ซ้ำกันให้ Insert อ่ะค่ะ

Imports System.Data.SqlClient
Imports System.IO
Public Class ClsAddUser
#Region "Fields and Properties"
    Private _vc_UserId As String
    Property vc_UserId
        Get
            Return _vc_UserId
        End Get
        Set(ByVal value)
            _vc_UserId = value
        End Set
    End Property
    Private _vc_Name As String
    Property vc_Name
        Get
            Return _vc_Name
        End Get
        Set(ByVal value)
            _vc_Name = value
        End Set
    End Property
    Private _vc_Position As String
    Property vc_Position
        Get
            Return _vc_Position
        End Get
        Set(ByVal value)
            _vc_Position = value
        End Set
    End Property
    Private _vc_Username As String
    Property vc_Username
        Get
            Return _vc_Username
        End Get
        Set(ByVal value)
            _vc_Username = value
        End Set
    End Property
    Private _vc_Password As String
    Property vc_Password
        Get
            Return _vc_Password
        End Get
        Set(ByVal value)
            _vc_Password = value
        End Set
    End Property
    Private _vc_Private As String
    Property vc_Private
        Get
            Return _vc_Private
        End Get
        Set(ByVal value)
            _vc_Private = value
        End Set
    End Property

#End Region
#Region "Constructors"
    Private Sub PopulateDefault()
        _vc_UserId = ""
        _vc_Name = ""
        _vc_Position = ""
        _vc_Username = ""
        _vc_Password = ""
        _vc_Private = ""
    End Sub
    Sub New()
        PopulateDefault()
    End Sub
#End Region
    Public sql As String
    Dim ConstrEV As String


    Public Function InsertUser_Admin() As Boolean
        ConnS.Open()

        'Dim intNumRows As Integer
        'sql = " SELECT COUNT(*) FROM M_Users WHERE vc_UserId = '" & AddUserID & "' "
        'cmd = New SqlCommand(sql, ConnS)
        'MessageBox.Show(sql)
        'intNumRows = cmd.ExecuteScalar()
        'If intNumRows > 0 Then
        '    MessageBox.Show("Fail")
        'Else
        sql = " INSERT INTO M_Users("
        sql += " vc_UserId, "
        sql += " vc_Name, "
        ''sql += " vc_Position)"
        'sql += " vc_Position, "
        sql += " vc_Username, "
        sql += " vc_Password, "
        sql += " vc_Private)"
        sql += " VALUES ("
        sql += "  @vc_UserId, "
        sql += "  @vc_Name, "
        ''sql += "  @vc_Position)"
        'sql += "  @vc_Position, "
        sql += "  @vc_Username, "
        sql += "  @vc_Password, "
        sql += "  @vc_Private)"
        Using cmd As New SqlCommand(sql)
            cmd.Parameters.AddWithValue("@vc_UserId", AddUserID)
            cmd.Parameters.AddWithValue("@vc_Name", InsertName)
            'cmd.Parameters.AddWithValue("@vc_Position", StatusUser)
            cmd.Parameters.AddWithValue("@vc_Username", InsertUserNm)
            cmd.Parameters.AddWithValue("@vc_Password", InsertPass)
            cmd.Parameters.AddWithValue("@vc_Private", StatusUser)
            MessageBox.Show("บันทึกสำเร็จ")
            InsertName = ""
            StatusUser = ""
            Return ExecuteNonQuery(cmd)
            ConnS.Close()
        End Using
'End if
    End Function

    
End Class