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Foreign key for multiple tables and columns?

I was studying foreign keys, and I wanted to know if I used it correctly in the following example:

CREATE TABLE user(
  id INT(11) NOT NULL AUTO_INCREMENT,
  username VARCHAR(50) NOT NULL,
  password VARCHAR(20) NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE items(
  i_id INT(11) NOT NULL AUTO_INCREMENT,
  name TINYTEXT NOT NULL,
  price DECIMAL(8,2) NOT NULL,
  PRIMARY KEY (i_id)
);

CREATE TABLE user_purchase(
  i_id INT(11) NOT NULL,
  name TINYTEXT NOT NULL,
  id INT(11) NOT NULL,
  FOREIGN KEY (i_id) REFERENCES items(i_id),
  FOREIGN KEY (name) REFERENCES items(name),
  FOREIGN KEY (id) REFERENCES user(id)
);

thanks

Now, how can I get the maximum information only from a foreign key if I use, say, PHP?

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2 answers

You do not need to include the element name in both tables. This is called a denormalized solution. You should have it only in the table of elements and refer only to the identifier, then if you need a name, you can also join it based on the primary key (id). Otherwise, this is quite normal, in my opinion.

CREATE TABLE user(
  id INT(11) NOT NULL AUTO_INCREMENT,
  username VARCHAR(50) NOT NULL,
  password VARCHAR(20) NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE items(
  i_id INT(11) NOT NULL AUTO_INCREMENT,
  name TINYTEXT NOT NULL,
  price DECIMAL(8,2) NOT NULL,
  PRIMARY KEY (i_id)
);

CREATE TABLE user_purchase(
  i_id INT(11) NOT NULL,
  name TINYTEXT NOT NULL,
  id INT(11) NOT NULL,
  FOREIGN KEY (i_id) REFERENCES items(i_id),
  FOREIGN KEY (id) REFERENCES user(id)
);

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+2

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CREATE TABLE `user`(
  id INT(11) NOT NULL AUTO_INCREMENT,
  username VARCHAR(50) NOT NULL,
  password VARCHAR(20) NOT NULL,
  PRIMARY KEY (id)
);

CREATE TABLE items(
  i_id INT(11) NOT NULL AUTO_INCREMENT,
  `name` TINYTEXT UNIQUE NOT NULL,
  price DECIMAL(8,2) NOT NULL,
  PRIMARY KEY (i_id)    
);

CREATE TABLE user_purchase(
  i_id INT(11) NOT NULL,
  `name` TINYTEXT NOT NULL,
  id INT(11) NOT NULL,
  FOREIGN KEY (i_id) REFERENCES items(i_id),
  FOREIGN KEY (id) REFERENCES `user`(id)    
);
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