Topic: Better sql construct in sales/includes/db/sales_order_db.inc
At the end of the file sales/includes/db/sales_order_db.inc we have:
function last_sales_order_detail($order, $field)
{
$sql = "SELECT $field
FROM ".TB_PREF."sales_order_details d
WHERE order_no =
(SELECT order_no FROM ".TB_PREF."sales_orders o
WHERE debtor_no=" . db_escape($order->customer_id) . "
ORDER BY order_no DESC LIMIT 1)
ORDER BY d.id DESC LIMIT 1";
$last_query=db_query($sql, "Could not retrieve last order detail");
$row = db_fetch_row($last_query);
return $row == false ? false : $row[0];
}Kindly change it to:
function last_sales_order_detail($order, $field)
{
$sql = "SELECT $field
FROM ".TB_PREF."sales_order_details d
LEFT JOIN " .TB_PREF."sales_orders o on d.order_no=o.order_no
WHERE debtor_no=" . db_escape($order->customer_id) . "
ORDER BY d.id DESC LIMIT 1";
$last_query=db_query($sql, "Could not retrieve last order detail");
$row = db_fetch_row($last_query);
return $row == false ? false : $row[0];
}It uses a left join instead of a secondary select.
The on d.order_no=o.order_no can become USING (order_no) to further optimise it.
