SQL/MySQL/Join/Join Table

NATURAL JOIN in MySQL

   <source lang="sql">

/* mysql> SELECT ArticleTitle, Copyright,

   ->    CONCAT_WS(" ", AuthorFirstName, AuthorMiddleName, AuthorLastName) AS Author
   -> FROM Articles AS b NATURAL JOIN AuthorArticle AS ab
   ->    NATURAL JOIN Authors AS a
   -> WHERE Copyright<1980
   -> ORDER BY ArticleTitle;

+-------------------+-----------+-------------------+ | ArticleTitle | Copyright | Author | +-------------------+-----------+-------------------+ | Buy a paper | 1932 | James Elk | | Buy a paper | 1932 | Mary G. Lee | | How write a paper | 1934 | Tom M Ride | | Sell a paper | 1966 | Henry S. Thompson | +-------------------+-----------+-------------------+ 4 rows in set (0.01 sec)

• /

Drop table Articles; Drop table Authors; Drop table AuthorArticle;

CREATE TABLE Articles (

  ArticleID SMALLINT NOT NULL PRIMARY KEY,
  ArticleTitle VARCHAR(60) NOT NULL,
  Copyright YEAR NOT NULL

) ENGINE=INNODB;

INSERT INTO Articles VALUES (12786, "How write a paper", 1934),

                           (13331, "Publish a paper", 1919),
                           (14356, "Sell a paper", 1966),
                           (15729, "Buy a paper", 1932),
                           (16284, "Conferences", 1996),
                           (17695, "Journal", 1980),
                           (19264, "Information", 1992),
                           (19354, "AI", 1993);

CREATE TABLE Authors (

  AuthID SMALLINT NOT NULL PRIMARY KEY,
  AuthorFirstName VARCHAR(20),
  AuthorMiddleName VARCHAR(20),
  AuthorLastName VARCHAR(20)

) ENGINE=INNODB;

INSERT INTO Authors VALUES (1006, "Henry", "S.", "Thompson"),

                          (1007, "Jason", "Carol", "Oak"),
                          (1008, "James", NULL, "Elk"),
                          (1009, "Tom", "M", "Ride"),
                          (1010, "Jack", "K", "Ken"),
                          (1011, "Mary", "G.", "Lee"),
                          (1012, "Annie", NULL, "Peng"),
                          (1013, "Alan", NULL, "Wang"),
                          (1014, "Nelson", NULL, "Yin");

CREATE TABLE AuthorArticle (

  AuthID SMALLINT NOT NULL,
  ArticleID SMALLINT NOT NULL,
  PRIMARY KEY (AuthID, ArticleID),
  FOREIGN KEY (AuthID) REFERENCES Authors (AuthID),
  FOREIGN KEY (ArticleID) REFERENCES Articles (ArticleID)

) ENGINE=INNODB;

INSERT INTO AuthorArticle VALUES (1006, 14356),

                             (1008, 15729), 
                             (1009, 12786), 
                             (1010, 17695),
                             (1011, 15729), 
                             (1012, 19264), 
                             (1012, 19354), 
                             (1014, 16284);
 

SELECT ArticleTitle, Copyright,

  CONCAT_WS(" ", AuthorFirstName, AuthorMiddleName, AuthorLastName) AS Author

FROM Articles AS b NATURAL JOIN AuthorArticle AS ab

  NATURAL JOIN Authors AS a

WHERE Copyright<1980 ORDER BY ArticleTitle;

      </source>
   
  

Two NATURAL JOIN in select command

   <source lang="sql">

/* mysql> SELECT ArticleTitle, Copyright,

   ->    CONCAT_WS(" ", AuthorFirstName, AuthorMiddleName, AuthorLastName) AS Author
   -> FROM Articles AS b NATURAL LEFT JOIN AuthorArticle AS ab
   ->    NATURAL LEFT JOIN Authors AS a
   -> WHERE Copyright<1980
   -> ORDER BY ArticleTitle;

+-------------------+-----------+-------------------+ | ArticleTitle | Copyright | Author | +-------------------+-----------+-------------------+ | Buy a paper | 1932 | James Elk | | Buy a paper | 1932 | Mary G. Lee | | How write a paper | 1934 | Tom M Ride | | Publish a paper | 1919 | | | Sell a paper | 1966 | Henry S. Thompson | +-------------------+-----------+-------------------+ 5 rows in set (0.01 sec)

• /

Drop table Articles; Drop table Authors; Drop table AuthorArticle;

CREATE TABLE Articles (

  ArticleID SMALLINT NOT NULL PRIMARY KEY,
  ArticleTitle VARCHAR(60) NOT NULL,
  Copyright YEAR NOT NULL

) ENGINE=INNODB;

INSERT INTO Articles VALUES (12786, "How write a paper", 1934),

                           (13331, "Publish a paper", 1919),
                           (14356, "Sell a paper", 1966),
                           (15729, "Buy a paper", 1932),
                           (16284, "Conferences", 1996),
                           (17695, "Journal", 1980),
                           (19264, "Information", 1992),
                           (19354, "AI", 1993);

CREATE TABLE Authors (

  AuthID SMALLINT NOT NULL PRIMARY KEY,
  AuthorFirstName VARCHAR(20),
  AuthorMiddleName VARCHAR(20),
  AuthorLastName VARCHAR(20)

) ENGINE=INNODB;

INSERT INTO Authors VALUES (1006, "Henry", "S.", "Thompson"),

                          (1007, "Jason", "Carol", "Oak"),
                          (1008, "James", NULL, "Elk"),
                          (1009, "Tom", "M", "Ride"),
                          (1010, "Jack", "K", "Ken"),
                          (1011, "Mary", "G.", "Lee"),
                          (1012, "Annie", NULL, "Peng"),
                          (1013, "Alan", NULL, "Wang"),
                          (1014, "Nelson", NULL, "Yin");

CREATE TABLE AuthorArticle (

  AuthID SMALLINT NOT NULL,
  ArticleID SMALLINT NOT NULL,
  PRIMARY KEY (AuthID, ArticleID),
  FOREIGN KEY (AuthID) REFERENCES Authors (AuthID),
  FOREIGN KEY (ArticleID) REFERENCES Articles (ArticleID)

) ENGINE=INNODB;

INSERT INTO AuthorArticle VALUES (1006, 14356),

                             (1008, 15729), 
                             (1009, 12786), 
                             (1010, 17695),
                             (1011, 15729), 
                             (1012, 19264), 
                             (1012, 19354), 
                             (1014, 16284);
 

SELECT ArticleTitle, Copyright,

  CONCAT_WS(" ", AuthorFirstName, AuthorMiddleName, AuthorLastName) AS Author

FROM Articles AS b NATURAL LEFT JOIN AuthorArticle AS ab

  NATURAL LEFT JOIN Authors AS a

WHERE Copyright<1980 ORDER BY ArticleTitle;

      </source>