MySQL: INNER JOIN query in an EITHER-OR situation - mysql

Question

I need to find all Users that belong to a certain Country (ID = 4321). But a User's Location can have...
EITHER a City
OR a Cityaddition, as you can see in...
The database schema:
User -< Locations >- City >- District >- Region >- Country
>- Cityaddition >- District >- Region >- Country
Legend: (read from left to right)
-< : "...has many..."
>- : "...has one..."
How do I have to modify my query below in order to make this EITHER-OR condition work in 1 single query?
(Currently, this query only selects Users that have BOTH a City AND a Cityaddition, which is never the case in reality.)
SELECT users.* FROM users
INNER JOIN locations ON locations.user_id = users.id
INNER JOIN cities ON cities.id = locations.city_id
INNER JOIN districts ON districts.id = cities.district_id
INNER JOIN regions ON regions.id = districts.region_id
INNER JOIN cityadditions ON cityadditions.id = locations.cityaddition_id
INNER JOIN districts
districts_cityadditions ON districts_cityadditions.id = cityadditions.district_id
INNER JOIN regions
regions_districts ON regions_districts.id = districts_cityadditions.region_id
WHERE (regions.country_id = 4321)

Answer 1

As a single query, you can do based on a parallel hierarchy and doing a logical NOT NULL on either side. Two separate via would be better as Barmar indicates due to the explicit OR.
Also, use aliases to shorten and make more readable and you can remove all those ticks. You typically only need those when dealing with column names that are also reserved words.
SELECT
u.*
FROM
users u
JOIN locations l
ON u.id = l.user_id
LEFT JOIN cities c
ON l.city_id = c.id
JOIN districts d
ON c.district_id = d.id
INNER JOIN regions r
ON d.region_id = r.id
AND r.country_id = 4321
LEFT JOIN cityadditions ca
ON l.cityaddition_id = ca.id
JOIN districts d2
ON ca.district_id = da.id
JOIN regions r2
ON d2.region_id = r2.id
AND r2.country_id = 4321
where
r.id IS NOT NULL
OR r2.id IS NOT NULL

Answer 2

Using UNION, but minimising code repetition, and the number of redundant joins...
The planner is also able to use indexing to minimise query cost
SELECT DISTINCT -- all queries MAY need this, depending on the structure of your data
`users`.*
FROM
`regions`
INNER JOIN
`districts`
ON `districts`.`region_id` = `regions`.`id`
INNER JOIN
(
SELECT
`locations`.`id`,
`cities`.`district_id`
FROM
`locations`
INNER JOIN
`cities`
ON `cities`.`id` = `locations`.`city_id`
UNION ALL
SELECT
`locations`.`id`,
`cityadditions`.`district_id`
FROM
`locations`
INNER JOIN
`cityadditions`
ON `cityadditions`.`id` = `locations`.`cityaddition_id`
)
AS `locations`
ON `locations`.`district_id` = `district`.`id`
INNER JOIN
`users`
ON `users`.`location_id` = `locations`.`id`
WHERE
`regions`.`country_id` = 4321