from-clause

If only one table-reference is specified, the intermediate result table is simply the result of that table-reference. If more than one table-reference is specified in the FROM clause, the intermediate result table consists of all possible combinations of the rows of the specified table-references (the Cartesian product). Each row of the result is a row from the first table-reference concatenated with a row from the second table-reference, concatenated in turn with a row from the third, and so on. The number of rows in the result is the product of the number of rows in all the individual table-references.