Struggling adding WHERE clause to INNER JOIN - php

Question

I have a query which is supposed to select the lowest price_per_pax_after_tax from every backend_hotels_id date_start and package_supplier and this appears to be working until I add a WHERE clause.
Here's the query:
SELECT e.price_per_pax_after_tax, e.hotel_score, e.package_id, e.package_type
FROM packages_sorted_YQU e
INNER JOIN (
SELECT db_id, MIN( price_per_pax_after_tax ) AS lowest_price, package_id, hotel_score
FROM `packages_sorted_YQU`
WHERE `package_type` IN ('9', '10', '18')
AND `package_duration` IN ('6', '8', '12')
GROUP BY
`date_start` , `package_supplier` , `backend_hotels_id`
) AS j
ON j.db_id = e.db_id
AND j.lowest_price= e.price_per_pax_after_tax
AND j.hotel_score = e.hotel_score
AND j.package_id = e.package_id;
The table is huge but all of the fields listed are INT except for date_start which is DATE
The where clause causing the problem is:
WHERE `package_type` IN ('9', '10', '18')
AND `package_duration` IN ('6', '8', '12')
Without the where clause I get over 400 results and with the where clause I get zero results :( Any help will be very much appreciated.

Answer 1

If your columns package_type and package_duration are of type int you don't have to wrap the values inside ' like strings.
SELECT e.price_per_pax_after_tax, e.hotel_score, e.package_id, e.package_type
FROM packages_sorted_YQU e
INNER JOIN (
SELECT db_id, MIN( price_per_pax_after_tax ) AS lowest_price, package_id, hotel_score
FROM `packages_sorted_YQU`
WHERE `package_type` IN (9, 10, 18)
AND `package_duration` IN (6, 8, 12)
GROUP BY
`date_start` , `package_supplier` , `backend_hotels_id`
) AS j
ON j.db_id = e.db_id
AND j.lowest_price= e.price_per_pax_after_tax
AND j.hotel_score = e.hotel_score
AND j.package_id = e.package_id;

Answer 2

The subquery:
SELECT db_id
, MIN( price_per_pax_after_tax ) AS lowest_price
, package_id
, hotel_score
FROM `packages_sorted_YQU`
WHERE `package_type` IN ('9', '10', '18')
AND `package_duration` IN ('6', '8', '12')
GROUP BY
`date_start`
, `package_supplier`
, `backend_hotels_id`
will yield indeterminate results, with or without the WHERE clause. Because you are grouping by date_start, package_supplier, backend_hotels_id and have in the SELECT list columns without any aggregate functions on them: db_id, package_id, hotel_score.
This query should work consistently if the (date_start, package_supplier, backend_hotels_id) is the Primary Key or Unique.
Which is the PRIMARY KEY of the table and are there any other UNIQUE keys?

Answer 3

Hi all and thank you for your valuable input. I've solved the problem without a sub-query and it works a bit faster too.
SELECT MIN
(
concat
(
LPAD(`price_per_pax_after_tax` , 5, '0'),
LPAD(`package_id` , 12, '0'),
LPAD(`hotel_score` , 7, '0')
)
) AS cat
FROM `packages_sorted_YQU`
WHERE `package_type` IN
(
9, 10, 18
)
AND `package_duration` IN
(
6, 7, 8
)
GROUP BY `date_start` , `package_supplier` , `backend_hotels_id`
Then in PHP I break apart the concatenation with:
while($r=mysql_fetch_array($q,MYSQL_ASSOC))
{
$a[lrp][] = intval(substr($r[cat], 0, 5));
$a[package_id][] = intval(substr($r[cat], 5, 12));
$a[hotel_score][] = substr($r[cat], 17, 7);
}
I was lucky that the only FLOAT value was the hotel_score so I put that last - the other two were of type INT