SQLite Joins: Cross Join

A cross join is a type of join in SQLite that returns the Cartesian product of two or more tables. The result set contains all combinations of rows from the tables involved in the join. This join is sometimes referred to as a cartesian join or a cross product join.

Syntax

The syntax for a cross join in SQLite is as follows:

SELECT * FROM table1 CROSS JOIN table2;

The CROSS JOIN keyword is used to join two or more tables, and the result set will contain all possible combinations of rows in the tables.

Example

Suppose we have two tables, employees and departments, where the employees table contains information about all the employees in the company and the departments table contains information about the different departments in the company. We can perform a cross join to get all possible combinations of employees and departments.

SELECT * FROM employees CROSS JOIN departments;

Output

The output of the above SQL query would be a result set containing all possible combinations of rows from the employees and departments tables.

employee_id | employee_name | department_id | department_name
------------+---------------+---------------+----------------
1           | John          | 1             | Sales
2           | Jane          | 1             | Sales
3           | Lisa          | 1             | Sales
1           | John          | 2             | Marketing
2           | Jane          | 2             | Marketing
3           | Lisa          | 2             | Marketing
1           | John          | 3             | Finance
2           | Jane          | 3             | Finance
3           | Lisa          | 3             | Finance

Explanation

In the example above, we perform a cross join between the employees and departments tables using the CROSS JOIN keyword. The result set contains all possible combinations of rows in the two tables.

The result set includes columns from both tables, with each column name prefixed with the name of the corresponding table. This is necessary because both tables may contain columns with the same name.

Use

A cross join can be useful in situations where you need to generate all possible combinations of rows from two or more tables. However, it's important to keep in mind that the result set can be very large, especially if the tables involved have a large number of rows.

Important Points

• A cross join returns the Cartesian product of two or more tables.
• The result set of a cross join contains all possible combinations of rows in the tables involved in the join.
• A cross join can be useful in situations where you need to generate all possible combinations of rows from two or more tables.
• The result set of a cross join can be very large, especially if the tables involved have a large number of rows.
• Be careful when using a cross join, as it can have a significant impact on performance.

Summary

In this tutorial, we learned about the Cross Join in SQLite, which is a join that returns the Cartesian product of two or more tables. We saw examples of using a cross join to get all possible combinations of employees and departments in a company. It's important to keep in mind the size of the result set when using a cross join, as it can have a significant impact on performance and can result in a very large result set.