题解 | #统计salary的累计和running_total#

# 题目：
# 按照salary的累计和running_total，其中running_total为前N个当前( to_date = '9999-01-01')
# 员工的salary累计和，其他以此类推
# 解析：本题考查了复用一张表，进行子查询，且与母表进行对比来确定在母表之前的所有子表的字段的总量
SELECT s.emp_no, s.salary,
(SELECT SUM(s1.salary) FROM salaries AS s1
WHERE s1.emp_no <= s.emp_no AND s1.to_date = "9999-01-01" ORDER BY s1.emp_no
) AS running_total
FROM salaries AS s
WHERE s.to_date = "9999-01-01"
ORDER BY s.emp_no