• 以两个连字符（—）为开头的注释。符号后跟着注释的文本。此文本不能扩展到新行，并以换行符结束注释。

       employee_id                                  -- employee id
       salary + NVL(commission_pct, 0),             -- total compensation
       job_id,                                      -- job
       departments d
  WHERE e.department_id = d.department_id
    AND salary + NVL(commission_pct, 0) >           -- whose compensation 
                                                    -- is greater than
          FROM employees 
          WHERE last_name = 'Pataballa')            -- of Pataballa
  ORDER BY last_name                                -- and order by last name
           employee_id                              -- and employee id.