Connecting two tables using third table with foreign key in mySQL - mysql

Question

I have three tables.
CREATE TABLE IF NOT EXISTS users (
userID int AUTO_INCREMENT,
username text NOT NULL,
password text NOT NULL,
PRIMARY KEY (userID)
);
CREATE TABLE IF NOT EXISTS schedule (
actID int AUTO_INCREMENT,
actName text NOT NULL,
actDay text NOT NULL,
actStart text NOT NULL,
actStop text NOT NULL,
PRIMARY KEY (actID)
);
CREATE TABLE IF NOT EXISTS connection (
userID int,
actID int,
FOREIGN KEY (userID) REFERENCES users(userID),
FOREIGN KEY (actID) REFERENCES schedule(actID)
);
I am using a third table (connection) to connect the first two tables (users and schedule) with FOREIGN KEY. How can I get all activities from schedule for a specific user?

Answer 1

If you want to search by user's name you must join all 3 tables:
select u.*, s.*
from users u
inner join connection c on c.userID = u.userID
inner join schedule s on s.actID = c.actID
where u.username = ?
If you want to search by user's id you must join only 2 tables:
select c.userID, s.*
from connection c inner join schedule s
on s.actID = c.actID
where c.userID = ?
If a user does not have any activities but you want in the results 1 row, with no activity then use left joins:
select u.*, s.*
from users u
left join connection c on c.userID = u.userID
left join schedule s on s.actID = c.actID
where u.username = ?