MySQL where condition based on select query - mysql

Question

I am having the following query to fetch the data from the table.
SELECT rental_plans.*,
( ( inventory.total_inventory
+ vehicles.tmp_qty ) - Ifnull(reservation.total_reserved, 0) ) AS
vehicle_inventory
FROM `rental_plans`
INNER JOIN `vehicles`
ON `vehicles`.`id` = `rental_plans`.`vehicle_id`
LEFT JOIN (SELECT Count(*) AS total_inventory,
vehicle_id
FROM vehicle_inventories
GROUP BY vehicle_id) AS inventory
ON `inventory`.`vehicle_id` = `vehicles`.`id`
LEFT JOIN (SELECT vehicle_id,
Sum(qty) AS total_reserved
FROM `reservations`
WHERE ( '2018-12-18' BETWEEN pickup_date AND drop_date )
OR ( '2018-12-28' BETWEEN pickup_date AND drop_date )
AND `status` NOT IN ( 'RETURNED' )
GROUP BY `vehicle_id`) AS `reservation`
ON `rental_plans`.`vehicle_id` = `reservation`.`vehicle_id`
WHERE `rental_plans`.`id` > 0
AND `rental_plans`.`pickup` = '1'
AND `rental_plans`.`drop` = '10'
ORDER BY `rental_plans`.`price` ASC
But I want to handle where condition based on vehicle_inventory.
I tried with ... AND vehicle_inventory > 16 order by `rental_plans`.`price` ASC but this generates the error that column not found in the table

Answer 1

The reason is that vehicle_inventory is an alias and it is resolved after WHERE clause. You can read about that here. You can do something like:
SELECT *
FROM (SELECT rental_plans.*,
( ( inventory.total_inventory
+ vehicles.tmp_qty ) - Ifnull(reservation.total_reserved, 0)
) AS
vehicle_inventory
FROM `rental_plans`
INNER JOIN `vehicles`
ON `vehicles`.`id` = `rental_plans`.`vehicle_id`
LEFT JOIN (SELECT Count(*) AS total_inventory,
vehicle_id
FROM vehicle_inventories
GROUP BY vehicle_id) AS inventory
ON `inventory`.`vehicle_id` = `vehicles`.`id`
LEFT JOIN (SELECT vehicle_id,
Sum(qty) AS total_reserved
FROM `reservations`
WHERE ( '2018-12-18' BETWEEN
pickup_date AND drop_date )
OR ( '2018-12-28' BETWEEN
pickup_date AND drop_date )
AND `status` NOT IN ( 'RETURNED' )
GROUP BY `vehicle_id`) AS `reservation`
ON `rental_plans`.`vehicle_id` =
`reservation`.`vehicle_id`
WHERE `rental_plans`.`id` > 0
AND `rental_plans`.`pickup` = '1'
AND `rental_plans`.`drop` = '10')a
WHERE a.rental_plans > 16
ORDER BY `price` ASC
or
SELECT rental_plans.*,
( (inventory.total_inventory + vehicles.tmp_qty) - Ifnull(reservation.total_reserved, 0) ) AS vehicle_inventory
FROM `rental_plans`
INNER JOIN `vehicles`
ON `vehicles`.`id` = `rental_plans`.`vehicle_id`
LEFT JOIN
(
SELECT Count(*) AS total_inventory,
vehicle_id
FROM vehicle_inventories
GROUP BY vehicle_id) AS inventory
ON `inventory`.`vehicle_id` = `vehicles`.`id`
LEFT JOIN
(
SELECT vehicle_id,
Sum(qty) AS total_reserved
FROM `reservations`
WHERE (
'2018-12-18' BETWEEN pickup_date AND drop_date)
OR (
'2018-12-28' BETWEEN pickup_date AND drop_date)
AND `status` NOT IN ('RETURNED')
GROUP BY `vehicle_id`) AS `reservation`
ON `rental_plans`.`vehicle_id` = `reservation`.`vehicle_id`
WHERE `rental_plans`.`id` > 0
AND `rental_plans`.`pickup` = '1'
AND `rental_plans`.`drop` = '10'
where (
inventory.total_inventory + vehicles.tmp_qty) - ifnull(reservation.total_reserved, 0) > 16
ORDER BY `rental_plans`.`price` ASC