SQL/MySQL/Join/Left Join
Содержание
LEFT JOIN tables
/*
mysql> SELECT ArticleTitle, Copyright, AuthID
-> FROM Articles AS b LEFT JOIN AuthorArticle AS ab
-> ON b.ArticleID=ab.ArticleID
-> ORDER BY ArticleTitle;
+-------------------+-----------+--------+
| ArticleTitle | Copyright | AuthID |
+-------------------+-----------+--------+
| AI | 1993 | 1012 |
| Buy a paper | 1932 | 1008 |
| Buy a paper | 1932 | 1011 |
| Conferences | 1996 | 1014 |
| How write a paper | 1934 | 1009 |
| Information | 1992 | 1012 |
| Journal | 1980 | 1010 |
| Publish a paper | 1919 | NULL |
| Sell a paper | 1966 | 1006 |
+-------------------+-----------+--------+
9 rows in set (0.02 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, AuthID
FROM Articles AS b LEFT JOIN AuthorArticle AS ab
ON b.ArticleID=ab.ArticleID
ORDER BY ArticleTitle;
Two LEFT JOIN
/*
mysql> SELECT ArticleTitle, Copyright, AuthorFirstName, AuthorMiddleName, AuthorLastName
-> FROM Articles AS b LEFT JOIN AuthorArticle AS ab ON b.ArticleID=ab.ArticleID
-> LEFT JOIN Authors AS a ON ab.AuthID=a.AuthID
-> ORDER BY ArticleTitle;
+-------------------+-----------+-----------------+------------------+----------------+
| ArticleTitle | Copyright | AuthorFirstName | AuthorMiddleName | AuthorLastName |
+-------------------+-----------+-----------------+------------------+----------------+
| AI | 1993 | Annie | NULL | Peng |
| Buy a paper | 1932 | James | NULL | Elk |
| Buy a paper | 1932 | Mary | G. | Lee |
| Conferences | 1996 | Nelson | NULL | Yin |
| How write a paper | 1934 | Tom | M | Ride |
| Information | 1992 | Annie | NULL | Peng |
| Journal | 1980 | Jack | K | Ken |
| Publish a paper | 1919 | NULL | NULL | NULL |
| Sell a paper | 1966 | Henry | S. | Thompson |
+-------------------+-----------+-----------------+------------------+----------------+
9 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, AuthorFirstName, AuthorMiddleName, AuthorLastName
FROM Articles AS b LEFT JOIN AuthorArticle AS ab ON b.ArticleID=ab.ArticleID
LEFT JOIN Authors AS a ON ab.AuthID=a.AuthID
ORDER BY ArticleTitle;
Two LEFT JOIN in select command
/*
mysql> SELECT ArticleTitle, Copyright, CONCAT_WS(" ", AuthorFirstName, AuthorMid
dleName, AuthorLastName) AS Author
-> FROM Articles AS b LEFT JOIN AuthorArticle AS ab ON b.ArticleID=ab.Articl
eID
-> LEFT JOIN Authors AS a ON ab.AuthID=a.AuthID
-> ORDER BY ArticleTitle;
+-------------------+-----------+-------------------+
| ArticleTitle | Copyright | Author |
+-------------------+-----------+-------------------+
| AI | 1993 | Annie Peng |
| Buy a paper | 1932 | James Elk |
| Buy a paper | 1932 | Mary G. Lee |
| Conferences | 1996 | Nelson Yin |
| How write a paper | 1934 | Tom M Ride |
| Information | 1992 | Annie Peng |
| Journal | 1980 | Jack K Ken |
| Publish a paper | 1919 | |
| Sell a paper | 1966 | Henry S. Thompson |
+-------------------+-----------+-------------------+
9 rows in set (0.03 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 LEFT JOIN AuthorArticle AS ab ON b.ArticleID=ab.ArticleID
LEFT JOIN Authors AS a ON ab.AuthID=a.AuthID
ORDER BY ArticleTitle;
"USING" command in LEFT JOIN
mysql> SELECT ArticleTitle, Copyright, AuthID
-> FROM Articles LEFT JOIN AuthorArticle
-> USING (ArticleID)
-> ORDER BY ArticleTitle;
+-------------------+-----------+--------+
| ArticleTitle | Copyright | AuthID |
+-------------------+-----------+--------+
| AI | 1993 | 1012 |
| Buy a paper | 1932 | 1008 |
| Buy a paper | 1932 | 1011 |
| Conferences | 1996 | 1014 |
| How write a paper | 1934 | 1009 |
| Information | 1992 | 1012 |
| Journal | 1980 | 1010 |
| Publish a paper | 1919 | NULL |
| Sell a paper | 1966 | 1006 |
+-------------------+-----------+--------+
9 rows in set (0.00 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, AuthID
FROM Articles LEFT JOIN AuthorArticle
USING (ArticleID)
ORDER BY ArticleTitle;