Question

I have a table with following structure,

+-----------------------+------------------+------+-----+---------+----------------+
| Field                 | Type             | Null | Key | Default | Extra          |
+-----------------------+------------------+------+-----+---------+----------------+
| location_id           | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| name                  | varchar(60)      | NO   |     | NULL    |                |
| city_id               | int(10) unsigned | NO   | MUL | NULL    |                |
| parent_location_id    | int(11)          | NO   |     | NULL    |                |
+-----------------------+------------------+------+-----+---------+----------------+

Here one location may or may not have a parent_location_id, which is another row in the same table.

Now I want to select all location which have atleast one sublocation. I have the following query. Is it correct?

SELECT DISTINCT (
   a.location_id
), a.name, a.is_delivery_available, a.is_booking_available
FROM  `locations` a
JOIN  `locations` b ON a.location_id = b.parent_location_id
WHERE a.`city_id` =5
ORDER BY a.name ASC 

Answer 1

use LEFT JOIN instead of INNER JOIN

SELECT  a.location_id
        a.name, 
        a.is_delivery_available, 
        a.is_booking_available
FROM   `locations` a
            LEFT JOIN  `locations` b 
                ON a.location_id = b.parent_location_id
WHERE a.`city_id` = 5
ORDER BY a.name ASC