RATIO_TO_REPORT是一个分析函数. 用来计算一个值在一系列值之间所占的比重.

语法：RATIO_TO_REPORT(列名或表达式) OVER()

下面的例子计算每一个采购员的工资在所有采购员中占的比率:

SELECT last_name, salary, RATIO_TO_REPORT(salary) OVER () AS rr
   FROM employees
   WHERE job_id = '采购员';
   
结果:
LAST_NAME                     SALARY         RR
------------------------- ---------- ----------
Khoo                            3100 .223021583
Baida                           2900 .208633094
Tobias                          2800 .201438849
Himuro                          2600  .18705036
Colmenares                      2500 .179856115