'If two tables in a join query have no join condition, then Oracle returns their Cartesian product. Oracle combines each row of one table with each row of the other.
A Cartesian product always generates many rows and is rarely useful.
For example, the Cartesian product of two tables, each with 100 rows, has 10,000 rows. Always include a join condition unless you specifically need a Cartesian product. If a query joins three or more tables and you do not specify a join condition for a specific pair, then the optimizer may choose a join order that avoids producing an
intermediate Cartesian product.'