Cross Join - (PostgreSQL Join)

Cross join or cartesian join is a type of join operation in PostgreSQL where all the possible combinations of rows from the two tables are returned. In this tutorial, we'll discuss the syntax, example, output, explanation, use, important points, and summary of cross join in PostgreSQL.

Syntax

SELECT *
FROM table1
CROSS JOIN table2;

Example

Let's see an example of cross join in PostgreSQL.

SELECT *
FROM products
CROSS JOIN categories;

The output of this query would return all possible combinations of rows between the "products" and "categories" tables.

Explanation

In the above example, a cross join is performed between the "products" and "categories" tables. This will return all possible combinations of rows between the two tables. In other words, it returns every combination of one row from the "products" table with every row from the "categories" table.

Use

Cross join is used when you need to combine every row in one table with every row in another table. It's useful in scenarios such as generating test data or creating a matrix of all possible combinations.

Important Points

• Cross join returns a cartesian product of two tables.
• Cross join produces a result set that is the size of the first table multiplied by the size of the second table.
• Cross join is not suitable for larger tables and can produce a large number of rows.

Summary

In this tutorial, we discussed the syntax, example, output, explanation, use, and important points of cross join in PostgreSQL. We learned that cross join returns all possible combinations of rows from two tables. It's used when you need to generate test data or create a matrix of all possible combinations between two tables. However, it's important to use cross join with caution as it can produce a large number of rows that can impact performance.