SQL中的交叉连接CROSS JOIN

SQL CROSS JOIN

SQL CROSS JOIN will return all records where each row from the first table is combined with each row from the second table. Which also mean CROSS JOIN returns the Cartesian product of the sets of rows from the joined tables.

A CROSS JOIN can be specified in two ways: using the JOIN syntax or by listing the tables in the FROM clause separated by commas without using a WHERE clause to supply join criteria.

SQL CROSS JOIN syntax:

SELECT * FROM [TABLE 1] CROSS JOIN [TABLE 2]

OR

SELECT * FROM [TABLE 1], [TABLE 2]

EXAMPLE :

Let's try with 2 tables below:

Table 1: GameScores

PlayerName	DepartmentId	Scores
Jason	1	3000
Irene	1	1500
Jane	2	1000
David	2	2500
Paul	3	2000
James	3	2000

Table 2: Departments

DepartmentId	DepartmentName
1	IT
2	Marketing
3	HR

SQL statement :

SELECT* FROM GameScores CROSS JOIN Departments 

Result:

PlayerName	DepartmentId	Scores	DepartmentId	DepartmentName
Jason	1	3000	1	IT
Irene	1	1500	1	IT
Jane	2	1000	1	IT
David	2	2500	1	IT
Paul	3	2000	1	IT
James	3	2000	1	IT
Jason	1	3000	2	Marketing
Irene	1	1500	2	Marketing
Jane	2	1000	2	Marketing
David	2	2500	2	Marketing
Paul	3	2000	2	Marketing
James	3	3000	2	Marketing
Jason	1	3000	3	HR
Irene	1	1500	3	HR
Jane	2	1000	3	HR
David	2	2500	3	HR
Paul	3	2000	3	HR
James	3	3000	3	HR

from:http://www.sqlguides.com/sql_cross_join.php