SQL Select Many to Many - mysql

Question

I'm using MYSQL 5.X and I'm having trouble figuring out a Query;
I have 2 entities with a many to many relationship.
client and service, therefore I have 3 tables:
clients, clients_has_services and services.
I need to Select EVERY Service that is NOT related to a particular client.
for example:
I have client with ID 1, and 4 Services in Total (Service1, Service2, Service3, Service4), client 1 has a relationship with Service1) so I need to retrieve all Other services (Service2, Service3, Service4)
Suggestions?

Answer 1

First, get a set all services.
Join that to the row from clients for the "particular client", so you have a set of all services for the client.
The "trick" is to use an anti-join pattern to exclude rows where you have "matches" in the clients_have_services table.
If you have the unique identifier for the client (and you only need the list for a single client), something like this:
SELECT s.*
FROM services s
LEFT
JOIN clients_have_services h
ON h.service_id = s.id
AND h.client_id = 42
WHERE h.service_id IS NULL
ORDER BY s.id
The outer join returns all rows from services, along with any "matching" rows from the clients_have_services table. The "trick" is the predicate in the WHERE clause that excludes any rows where a match was found, leaving just the services that are not related to the particular client.
If you are doing this for multiple clients... you'd need to also return the client cross joined with services (as cross product of clients and services), and then exclude the matches.
For example:
SELECT c.id AS client_id
, s.*
FROM clients c
CROSS
JOIN services s
LEFT
JOIN clients_have_services h
ON h.service_id = s.id
AND h.client_id = c.id
WHERE h.service_id IS NULL
ORDER BY c.id, s.id
There are a couple of other query patterns that will return an equivalent result, for example, a NOT EXISTS
SELECT s.*
FROM services s
WHERE NOT EXISTS
( SELECT 1
FROM clients_have_services h
WHERE c.client_id = 42
AND h.service_id = s.id
)
ORDER BY s.id

Answer 2

Assuming that your client_has_services rectifies the many-to-many so you have one to many on both sides, so your client_has_services should have:
ID (Key), Client_ID, Service_ID
SELECT * FROM services WHERE services.id != ANY (select client_has_services.services_id from client_has_services where client_has_services.client_id = ID_num_provided)