How to prevent duplicate entry to database

[Satyam_1]

Hi, I have an vb.net application linked to Oledb database.
here is my code in Button_Click event to prevent duplicate entry with same ID, ID is not the primary key in database.
Although it shows "Record Already" Exists", but I am not able to save data with new ID, to the database.
So what to do?

Try
            'Set up connection string
            Dim cnString As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\Satyam\Documents\Pathology.accdb"
            Dim sqlQRY As String = "SELECT COUNT(*) AS numRows FROM MPRecordIDSP WHERE ID = '" & IDtxt.Text & "'"
            Dim queryResult As Integer

            'Create connection
            Dim conn As OleDbConnection = New OleDbConnection(cnString)
            ' Open connection
            conn.Open()
            ' Query the database
            Dim com As New OleDbCommand(sqlQRY, conn)
            queryResult = com.ExecuteScalar()

            ' Close connection
            conn.Close()

            If queryResult > 0 Then

                MessageBox.Show("Already Exists!", "MP Register", MessageBoxButtons.OK, MessageBoxIcon.Information)
            Else
                com = New OleDbCommand("insert into MPRecordIDSP (Dt,ID,PatientName,Ward,RegNo,Age,Sex,Result,ReportedBy) values ('" & Dttxt.Text & "','" & IDtxt.Text & "','" & PatientNametxt.Text & "','" & Wardtxt.Text & "','" & RegNotxt.Text & "','" & Agetxt.Text & "','" & Sextxt.Text & "','" & Resulttxt.Text & "','" & ReportedBytxt.Text & "') ", conn)
            End If

        Catch ex As OleDbException
            MessageBox.Show("Customer Not found" + ex.Message)
        End Try

[adam_k]

In the Else part of the if..end if you are only setting the com, you are not executing it. Try executing the command you've just set.

[Satyam_1]

can you just pl modify the code for me.