Cross-Join

A cross join in SQL, also known as a Cartesian product, is a join operation that produces the combination of every row of the first table with every row of the second table.

If the first table has 'n' rows and the second table has 'm' rows, the result of the cross join will contain n*m rows. Note that there's no "ON" condition in a cross join, as it does not require any condition to join tables.

Here's an example of a cross join:

In this example, if the Customers table has 50 rows (i.e., 50 customers), and the Products table has 20 rows (i.e., 20 products), the result of the cross join will be 1000 rows, each one being a combination of each customer with each product.

It's worth noting that cross joins can result in very large result sets, and so they can consume significant amounts of resources and time. Therefore, they should be used carefully and appropriately.

While cross joins are less commonly used than other types of joins, they are useful when you want to generate all possible combinations between two sets of data, such as when creating combinations of colors and sizes for a list of products.