PHP实现n：m关系

Question

As to implement a N:M relationship of tables USERS (PK: user_id which is auto increment INT) and REQUESTS (PK: request_id which is auto increment INT), I've created the intermediate table USERS_GROUPS (PKs: two FKs US_userid, US_requestid which coincide with the PKs of USERS and REQUESTS ). When a user creates a new request I have to create a new record inside REQUESTS .

INSERT INTO REQUESTS (...) VALUES (...);

At the same time I want to create a new record inside USERS_GROUPS as to join USERS_GROUPS with USERS and REQUESTS . The value of the first FK pointed to USERS is known to me, however how may I find the value of the second FK pointed to the record I've just created?

In other words, I want to find the value of the field request_id of the record I've just created. This seems a little bit confusing to me and I don't know how to implement it.

INSERT INTO USERS_GROUPS (US_userid,US_request_id) VALUES (...,?????);

This is my first serious db schema I've ever created and my first n:m relationship I have to manage. Is my point of view correct? If yes, I 'd appreciate your help in how to realise it. If not which is the right approach?

Answer 1

You can use last-insert-id to retrieve the newly created id.

The library you use to connect to database usually has a function for it, such as mysqli_insert_id or PDO::lastInsertId .

Sidenote: Because you are performing multiple (independent) queries on the database it may be necessary to wrap it all in transaction.