my $found_id = undef;
my $sql = <<SQLCODE
  SELECT id
  FROM track 
  WHERE url = ?
SQLCODE

my $sth = $dbh->prepare( $sql );
if ( $sth && $sth->execute( $url ) )
{
    if ( my $row = $sth->fetchrow_arrayref() )
    {
        $found_id = $row->[0];
    }
}
else
{
    die( "Database error " . $dbh->errstr . "\n" );
}

if ( $found_id )
{
    # perform update
    $sql = <<SQLCODE;
  UPDATE user SET
    view = view + 1,
    last_ip = ?,
    last_time = ?
  WHERE
    id = ?
SQLCODE

    my $sth = $dbh->prepare( $sql );
    if ( $sth && $sth->execute( $last_ip, time(), $found_id ) )
    {
        if ( my $row = $sth->fetchrow_arrayref() )
        {
            $found_id = $row->[0];
        }
    }
    else
    {
        die( "Database error " . $dbh->errstr . "\n" );
    }
}
else
{
    # perform insert
    # code left to read as an exercise
}