Mysql Cross Join help.

[superbK]

Hi,

I am learning MySQL.
I am stuck with the Join statements specially with Cross Joins.
Can some one help me with the working of this Cross Join (Cartesian Product Join).

Thanks in advance.
superbK

[Sid-O]

Beginning with Joins

Basically it is the combining of two rows based on the comparative values in selected columns. This 'super-row' exists only for the duration of the query that creates it.

Cross-Join

Syntax:

SELECT <column_name> 
FROM <table1>, <table2>

A cross-join between two tables takes the data from each row in table1 and joins it to the data from each row in table2.

[Jkbaseball]

Mysql Cross Join

Cross Join is also called Cartesian Product Join. The Cross Join in SQL return you a result table in which each row from the first table is combined with each rows from the second table. In other words, you can say it is the cross multiplication of number of rows in each table. The Syntax used to represent Cross Join in Mysql :

select * from table1 cross join table 2;

Example

[Darth]

Have a look at this example:

/*

mysql> SELECT ArticleTitle, AuthID FROM Articles CROSS JOIN AuthorArticle;
+-------------------+--------+
| ArticleTitle      | AuthID |
+-------------------+--------+
| How write a paper |   1006 |
| Publish a paper   |   1006 |
| Sell a paper      |   1006 |
| Buy a paper       |   1006 |
| Conferences       |   1006 |
| Journal           |   1006 |
| Information       |   1006 |
| AI                |   1006 |
| How write a paper |   1008 |
| Publish a paper   |   1008 |
| Sell a paper      |   1008 |
| Buy a paper       |   1008 |
| Conferences       |   1008 |
| Journal           |   1008 |
| Information       |   1008 |
| AI                |   1008 |
| How write a paper |   1009 |
| Publish a paper   |   1009 |
| Sell a paper      |   1009 |
| Buy a paper       |   1009 |
| Conferences       |   1009 |
| Journal           |   1009 |
| Information       |   1009 |
| AI                |   1009 |
| How write a paper |   1010 |
| Publish a paper   |   1010 |
| Sell a paper      |   1010 |
| Buy a paper       |   1010 |
| Conferences       |   1010 |
| Journal           |   1010 |
| Information       |   1010 |
| AI                |   1010 |
| How write a paper |   1011 |
| Publish a paper   |   1011 |
| Sell a paper      |   1011 |
| Buy a paper       |   1011 |
| Conferences       |   1011 |
| Journal           |   1011 |
| Information       |   1011 |
| AI                |   1011 |
| How write a paper |   1012 |
| Publish a paper   |   1012 |
| Sell a paper      |   1012 |
| Buy a paper       |   1012 |
| Conferences       |   1012 |
| Journal           |   1012 |
| Information       |   1012 |
| AI                |   1012 |
| How write a paper |   1012 |
| Publish a paper   |   1012 |
| Sell a paper      |   1012 |
| Buy a paper       |   1012 |
| Conferences       |   1012 |
| Journal           |   1012 |
| Information       |   1012 |
| AI                |   1012 |
| How write a paper |   1014 |
| Publish a paper   |   1014 |
| Sell a paper      |   1014 |
| Buy a paper       |   1014 |
| Conferences       |   1014 |
| Journal           |   1014 |
| Information       |   1014 |
| AI                |   1014 |
+-------------------+--------+
64 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, AuthID FROM Articles CROSS JOIN AuthorArticle;

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