CREATE TABLE article (
price INT(30) NOT NULL,
published_on DATE NOT NULL,
article_id INT(30) NOT NULL,
CONSTRAINT pk_article_id PRIMARY KEY(article_id)
);
CREATE TABLE tag(
descption VARCHAR(30) NOT NULL,
priority INT(30) NOT NULL,
tag_id INT(30) NOT NULL,
CONSTRAINT pk_tag_article PRIMARY KEY(tag_id),
CONSTRAINT fk_tag_article FOREIGN KEY(tag_id) REFERENCES article(article_id)
);
INSERT INTO article VALUES (10.0, "2001-01-01", 0);
INSERT INTO article VALUES (20.0, "1992-05-08", 1);
INSERT INTO tag VALUES ("wtf", 1, 1);
INSERT INTO tag VALUES ("is this", 2, 2);
This is a relationship one to one.
I'm saying here that the primary key of the tag is the same from article.