Show multiple joined rows

Question

I have a simple relational MySQL database with users, cars an a log table. Everything works fine. In the log table I want to 'register' the users of a car. But a car can have two users at the same time.

My question: How can I show multiple users in the log table, using the relational database?

My database structure:

Table users

user_id  name   phone
-------  -----  -----
1        john   123
2        kevin  456

---

Table cars

car_id  nr   brand
------  ---  -----
1       666  Ford
2       999  Dodge

---

Table log

log_id  car_id  user_id1  user_id2
------  ------  --------  --------
1       1       1         2

---

The car.car_id is related to log.car_id and users.user_id is related to log.user_id1 and log.user_id2.

Supposed SQL:

SELECT log.*, cars.*, users.*
FROM log
LEFT JOIN cars ON log.car_id=car.car_id
LEFT JOIN users ON log.user_id1=users.user_id
LEFT JOIN users ON log.user_id2=users.user_id

PHP (in loop of course):

echo $row["brand"];
echo $row["name"]; // user_id1
echo $row["name"]; // user_id2

It's working for only one name. How to show the names of user_id1 and user_id2 in the same "log" row?

Answer 1

Try using aliases like this:

SELECT l.*, c.*, u1.*, u2.*
FROM log l
LEFT JOIN cars c ON l.car_id=c.car_id
LEFT JOIN users u1 ON l.user_id1=u1.user_id
LEFT JOIN users u2 ON l.user_id2=u2.user_id

(Note that it's bad practice to use "SELECT *" except for ad-hoc queries. So you should instead enumerate the exact columns you want to select.)