VS 2010 How to check if record already exists to avoid data redundancy

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Imports System.Data.OleDb
Public Class Form1
Public connstring As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Documents\tablename.accdb"
Public conn As New OleDbConnection(connstring)

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

If conn.State = ConnectionState.Closed Then
conn.Open()
MsgBox("connection is open", vbInformation)
Else
MsgBox("connection is close", vbCritical)
End If

End Sub

Private Sub Search_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Search.Click


If txtsearch.Text = Nothing Then
MsgBox("nothing to search", vbCritical)

Else
Dim myadapter As New OleDbDataAdapter("SELECT * FROM fullname WHERE ID = " & txtsearch.Text, conn)
Dim mytable As New DataTable
myadapter.Fill(mytable)
If mytable.Rows.Count > 0 Then
Me.txtid.Text = mytable.Rows(0).Item("ID")
Me.txtfname.Text = mytable.Rows(0).Item("fname")
Me.txtmname.Text = mytable.Rows(0).Item("mname")
Me.txtlname.Text = mytable.Rows(0).Item("lname")
Else
MsgBox("No Record Found", vbCritical, "Search")
End If
End If

End Sub

Private Sub btnadd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnadd.Click


Dim myadapter As New OleDbDataAdapter("INSERT INTO fullname ( fname, mname, lname) VALUES ('" & txtfname.Text & "', '" & txtmname.Text & "', '" & txtlname.Text & "')", conn)
Dim mytable As New DataTable
myadapter.Fill(mytable)


End Sub

End Class

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