ASA SQL User's Guide
  Joins: Retrieving Data from Several Tables

Cross joins

A cross join of two tables produces all possible combinations of rows from the two tables. A cross join is also called a cross product or Cartesian product.

Each row of the first table appears once with each row of the second table. Hence, the number of rows in the result set is the product of the number of rows in the first table and the number of rows in the second table, minus any rows that are omitted because of restrictions in a WHERE clause.

You cannot use an ON phrase with cross joins. However, you can put restrictions in a WHERE clause.

Inner and outer modifiers do not apply to cross joins 

Except in the presence of additional restrictions in the WHERE clause, all rows of both tables always appear in the result set of cross joins. Thus, the keywords INNER, LEFT OUTER and RIGHT OUTER are not applicable to cross joins.

For example, the following statement joins two tables.

SELECT *
FROM A CROSS JOIN B

The result set from this query includes all columns in A and all columns in B. There is one row in the result set for each combination of a row in A and a row in B. If A has n rows and B has m rows, the query returns n x m rows.

Commas