SQL CROSS JOIN

Consider the two tables below:

Student

StudentCourse

CARTESIAN JOIN: The CARTESIAN JOIN is also known as CROSS JOIN. In a CARTESIAN JOIN there is a join for each row of one table to every row of another table. This usually happens when the matching column or WHERE condition is not specified.

• In the absence of a WHERE condition the CARTESIAN JOIN will behave like a CARTESIAN PRODUCT . i.e., the number of rows in the result-set is the product of the number of rows of the two tables.

• In the presence of WHERE condition this JOIN will function like a INNER JOIN.

• Generally speaking, Cross join is similar to an inner join where the join-condition will always evaluate to True

Syntax:

SELECT table1.column1 , table1.column2, table2.column1...
FROM table1
CROSS JOIN table2;

table1: First table.
table2: Second table

Example Queries (CARTESIAN JOIN):

• In the below query we will select NAME and Age from Student table and COURSE_ID from StudentCourse table. In the output you can see that each row of the table Student is joined with every row of the table StudentCourse. The total rows in the result-set = 4 * 4 = 16.

  SELECT Student.NAME, Student.AGE, StudentCourse.COURSE_ID
  FROM Student
  CROSS JOIN StudentCourse;

Output :