CREATE TABLE usager(
  nomUsager VARCHAR(20) PRIMARY KEY,
  motDePasse VARCHAR(20) NOT NULL
);

CREATE TABLE motCle(
  keyword VARCHAR(50) PRIMARY KEY
);

CREATE TABLE article(
  id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
  titre VARCHAR(100),
  texte TEXT,
  nomUsager VARCHAR(20), 
  FOREIGN KEY (nomUsager) REFERENCES usager(nomUsager) 
);

CREATE TABLE article_motsCle(
  idArticle SMALLINT UNSIGNED,
  keyword VARCHAR(50),
  PRIMARY KEY (idArticle, keyword),
  FOREIGN KEY (idArticle) REFERENCES article(id),
  FOREIGN KEY (keyword) REFERENCES motCle(keyword)
);

所有的插入都起作用了，除了一个插入到article\u motscle表中

INSERT INTO article_motsCle VALUES
(1, "neutron stars");

出现错误#1452-无法添加或更新子行：外键约束失败。