MySQL 8.0

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CREATE TABLE User (userId INT AUTO_INCREMENT PRIMARY KEY, 
                   firstName VARCHAR(10))
INSERT INTO User (firstName) VALUES ('Bob'), ('Mike'), ('Bell'), ('Rogers')
CREATE TABLE Follow (followID INT AUTO_INCREMENT PRIMARY KEY,
                     follower INT,
                     following INT)
INSERT INTO Follow (follower, following) VALUES
(2, 3), (1, 4), (1, 3), (3, 1)
CREATE TABLE Tweet (tweetID INT AUTO_INCREMENT PRIMARY KEY,
                    userID INT,
                    tweet VARCHAR(50))
INSERT INTO Tweet (userID, tweet) VALUES
(1, 'Hello'),
(4, 'Hey'),
(1, 'Hi Folks!'),
(2, 'How are you'),
(2, 'Stackoverflow'),
(4, 'Something'),
(3, 'Heya!')
SELECT DISTINCT t.*
FROM User u
JOIN Follow f ON f.follower = u.userID
LEFT JOIN Tweet t ON t.userID = u.userID OR t.userID = f.following
WHERE u.userID = 1


tweetID
userID
tweet


1
1
Hello

2
4
Hey

3
1
Hi Folks!

6
4
Something

7
3
Heya!