Help with a microblog (twitter clone) database structure? - mysql

Question

I'm working on an exercise that wants me to create a small twitter clone, with users, tweets and following system. Well, i came up with the following database structure:
CREATE TABLE tweets (
tweet_id INT NOT NULL AUTO_INCREMENT,
tweet VARCHAR(140) NOT NULL,
PRIMARY KEY (tweet_id)
) ENGINE=INNODB;
CREATE TABLE users (
user_id INT NOT NULL AUTO_INCREMENT,
user VARCHAR(255) NOT NULL,
password VARCHAR(40) NOT NULL,
email VARCHAR(255) NOT NULL,
PRIMARY KEY (user_id)
) ENGINE=INNODB;
CREATE TABLE user_tweets (
id INT NOT NULL AUTO_INCREMENT,
id_user INT NOT NULL,
id_tweet INT NOT NULL,
PRIMARY KEY(id),
FOREIGN KEY (id_tweet)
REFERENCES tweets(tweeth_id)
ON UPDATE NO ACTION ON DELETE NO ACTION,
FOREIGN KEY (id_user)
REFERENCES users(user_id)) ENGINE=INNODB;
CREATE TABLE followers (
id_user INT NOT NULL REFERENCES users (user_id),
id_following INT NOT NULL REFERENCES users (user_id),
PRIMARY KEY (id_user, id_following)
) ENGINE=INNODB;
Is it valid? Am i missing something? Also:
How do i select the tweets from a user?
How do i select the followers from a user?
How do i select the people a user is following?
I'm getting a little lost with the foreign key concept. :(

Answer 1

Building on the answer by #Karel,
I'd use slightly different tables:
CREATE TABLE tweets (
tweet_id INT NOT NULL AUTO_INCREMENT,
user_id INT NOT NULL
tweet VARCHAR(140) NOT NULL,
PRIMARY KEY (tweet_id),
FOREIGN KEY user_id(user_id) REFERENCES users(user_id)
ON UPDATE CASCADE ON DELETE CASCADE
) ENGINE=INNODB;
CREATE TABLE users (
user_id INT NOT NULL AUTO_INCREMENT,
user VARCHAR(255) NOT NULL,
/*password VARCHAR(40) NOT NULL,*/<<--- NEVER STORE A PASSWORD IN THE CLEAR!
passhash VARCHAR(40) NOT NULL,
email VARCHAR(255) NOT NULL,
PRIMARY KEY (user_id)
) ENGINE=INNODB;
CREATE TABLE followers (
id_user INT NOT NULL REFERENCES users (user_id),
id_following INT NOT NULL REFERENCES users (user_id),
PRIMARY KEY (id_user, id_following)
) ENGINE=INNODB;
How do i select the tweets from a user?
SELECT * FROM tweets WHERE user_id = 458
How do i select the followers from a user?
SELECT * FROM users
INNER JOIN followers ON (users.users_id = followers.id_user)
WHERE followers.id_following = 458
How do i select the people a user is following?
SELECT * FROM users
INNER JOIN followers ON (followers.id_following = users.user_id)
WHERE followers.id_user = 458
Use a SHA2 hash to compare the password.
And don't forget to add a salt to the hashing to prevent rainbow attacks.
SELECT user_id
FROM users
WHERE users.user = 'OralB'
AND users.passhash = SHA2(CONCAT(users.user,'secretToothbrush'),512)
SHA1 is no longer secure, so I'd advice using SHA2 with a 512bit hash length.
Links
MySQL tutorial: http://www.tizag.com/mysqlTutorial/
Foreign keys: http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html
SHA2: http://dev.mysql.com/doc/refman/5.5/en/encryption-functions.html#function_sha2
Concat: http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_concat
Why salt: What is "salt" when relating to MYSQL sha1?

Answer 2

You don't need a table 'user_tweet' because a tweet can only belong to 1 user, so it would be more logical to have a 'user_id' in you tweet-table
a crosstable like user_tweet is only useful when there is a many-to-many relationship (for example a teacher teaches multiple classgroups, classgroups get classes from multiple teachers)
if you do this you can select the tweets from a user by this sql-statement:
SELECT Tweet
FROM Tweets t (your table name)
WHERE t.User_ID == UserID_Whose_Tweets_you_want
you should now be able to get the followers with a similar query ;D
Hope you can do anything with this!