SQL CROSS JOIN

SQL CROSS JOIN returns the Cartesian product of two tables, combining each row from the first table with every row from the second table.

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1. Overview

SQL CROSS JOIN produces a result set that is the product of two or more tables, generating all possible combinations of rows. It does not require any matching condition and returns every row from the first table combined with every row from the second table.

Example:

// Example of using CROSS JOIN to retrieve Cartesian product of two tables
SELECT customers.customer_name, products.product_name
FROM customers
CROSS JOIN products;

This example retrieves the customer names along with the product names, combining every customer with every product.

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2. Syntax

The syntax for SQL CROSS JOIN is as follows:

SELECT columns
FROM table1
CROSS JOIN table2;

Where table1 and table2 are the tables to be joined, and the result set includes all possible combinations of rows from both tables.

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3. Usage

SQL CROSS JOIN is useful when you want to generate all possible combinations of rows from multiple tables, such as when creating a Cartesian product. However, it can lead to a large result set if the tables involved have many rows.

Example:

// Example of using CROSS JOIN to retrieve Cartesian product of two tables
SELECT customers.customer_name, products.product_name
FROM customers
CROSS JOIN products;

This example retrieves customer names along with product names, combining every customer with every product.

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4. Conclusion

SQL CROSS JOIN is a powerful tool for generating Cartesian products of multiple tables, producing all possible combinations of rows. While it can be useful in certain scenarios, it should be used judiciously to avoid generating excessively large result sets.