INNODB：在mysql表之间创建多对多的关系

Question

I have 2 tables, articles and entities table. An article can have many entities and an entity can belong to more than one category.

What would be the sql to create such an association in mysql such that I can insert an entity to the entities table via the articles table and be able to query for the article from the entities table.

The entity only has 2 fields, entity_id and entity while the articles table has 3 fields: article_id, url and category

Is this what I require to do

CREATE TABLE articles(
  article_id  INT NOT NULL AUTO_INCREMENT,
  url VARCHAR(255),
  category VARCHAR(255),
  PRIMARY KEY(article_id)
)ENGINE=INNODB;

CREATE TABLE entities(
  entity_id  INT NOT NULL AUTO_INCREMENT,
  entity VARCHAR(50),
  PRIMARY KEY(entity_id)
)

 CREATE TABLE relationships(
   relationship_id INT NOT NULL AUTO_INCREMENT,
   article_id INT,
   entity_id INT,
   PRIMARY KEY(relationship_id),
   FOREIGN KEY(article_id) references articles(article_id),
   FOREIGN KEY(entity_id) references entities(entity_id)
 )ENGINE=INNODB;

Answer 1

You need a third table that tracks the relationships between entity_id and article_id. When you want to make or change a relationship, you update this table.

[edit] This stackoverflow question may help you to understand, especially the most upvoted answer.