Cartesian product.

When a join condition is invalid or omitted completely, the result is a Cartesian product, in which all combinations of rows are displayed.

• All rows in the first table are joined to all rows in the second table.
  
  
• A cartesian product is formed when:
  - A join coindition is omitted
  - A join condition is invalid
  - All rows in the first table are joined to all rows in the second table
  
  
• To avoid a Cartesian product, always include a valid condition.
  

ex) SELECT last_name, department_name, dept_name FROM employees, departments;

  - No join condition is defined
  - The employees table has 20 rows and the departments table has 8 rows, so the result will have 160 rows.