SQLite Cross-Join

In SQLite, a cross-join is a type of join that returns the Cartesian product of two tables. This means that every row in the first table is combined with every row in the second table, resulting in a potentially large result set.

Syntax

The basic syntax of a cross-join in SQLite is as follows:

SELECT *
FROM table1
CROSS JOIN table2;

Here, table1 and table2 are the names of the tables to be cross-joined. The * symbol indicates that all columns from both tables should be returned in the result set.

Example

Suppose we have two tables students and courses, with the following data:

students

| id | name | |----|--------| | 1 | Alice | | 2 | Bob | | 3 | Charlie|

courses

| id | course | |----|--------| | 1 | Math | | 2 | English| | 3 | Physics|

To get the Cartesian product of these two tables using a cross-join, we can execute the following SQL statement:

SELECT *
FROM students
CROSS JOIN courses;

This would return the following result:

| id | name | id | course | |----|--------|----|---------| | 1 | Alice | 1 | Math | | 1 | Alice | 2 | English| | 1 | Alice | 3 | Physics | | 2 | Bob | 1 | Math | | 2 | Bob | 2 | English| | 2 | Bob | 3 | Physics | | 3 | Charlie| 1 | Math | | 3 | Charlie| 2 | English| | 3 | Charlie| 3 | Physics |

Here, every row in the students table is combined with every row in the courses table, resulting in a total of 9 rows.

Conclusion

In SQLite, a cross-join is useful when you need to combine every row of one table with every row of another table. However, this can result in a large result set, so be sure to use it only when necessary.