Not the way to add rows to a table

gistfile1.vb

    Public Shared Function GenerateNewUniqueID() As String
 
        Dim returnString As String = Guid.NewGuid.ToString()
        Dim unique As Boolean = False
 
        Using conn As New SqlConnection(My.Settings.onlinePDFConnectionString)
 
            conn.Open()
 
            Dim commString As String = "SELECT Count(*) FROM Books WHERE UniqueID = '{0}%'"
            Dim comm As New SqlCommand(String.Format(commString, returnString.Substring(0, 13)), conn)
 
            While Not unique
 
                comm.CommandText = String.Format(commString, returnString.Substring(0, 13))
                Dim count As Integer = comm.ExecuteScalar()
 
                If count > 0 Then
                    returnString = Guid.NewGuid.ToString()
                Else
                    unique = True
                End If
 
            End While
 
        End Using
 
        Return returnString
 
    End Function