The FROM clause specifies an intermediate result table.
If only one table-reference is specified, the intermediate result table is the result of that table-reference. If more than one table-reference is specified, the intermediate result table consists of all possible combinations of the rows of the specified table-reference (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. For a description of table-reference, see table-reference.