cume_dist
如果按升序排列，则统计：小于等于当前值的行数/总行数(number of rows ≤ current row)/(total number of rows）。如果是降序排列，则统计：大于等于当前值的行数/总行数。
示例：
1. 统计小于等于当前工资的人数占总人数的比例。
SELECT name,
dept_no,
salary,
cume_dist() OVER (ORDER BY salary) as cume_dist
FROM data;
结果：
+-------+-------+------+---------+
|name |dept_no|salary|cume_dist|
+-------+-------+------+---------+
|rose |2 |4000 |0.125 |
|jack |2 |5000 |0.375 |
|steven |3 |5000 |0.375 |
|john |1 |6000 |0.5 |
|jerry |2 |6600 |0.625 |
|tom |1 |8000 |0.75 |
|richard|3 |9000 |0.875 |
|mike |1 |10000 |1.0 |
+-------+-------+------+---------+如果要统计大于等于当前工资的人数占总人数的比例，只需更改salary排序规则为降序desc即可。
2. 根据部门统计小于等于当前工资的人数占部门总人数的比例
SELECT
name,
dept_no,
salary,
cume_dist() OVER (PARTITION BY dept_no ORDER BY salary) as cume_dist
FROM data;