mysql - Mysql中联合三张表

Question

我有三张表employee，promotion和punishment 员工的表结构是这样的

Id       int
Fullname     varchar
...............
promotionDate       date

Promotion的表结构是这样的 标识整数 emp_id 整型 datedate日期

惩罚的表结构是这样的

id                  int
emp_id              int
direcotorateDate    date

假设employee表有200条记录，每个月有一组员工升职(在职一年后)，我想获取当月所有升职员工的列表 我可以通过这个查询轻松获取列表

SELECT * 
FROM employee 
WHERE MONTH(promotionDate) = MONTH(CURRENT_DATE())
   AND YEAR(promotionDate) = YEAR(CURRENT_DATE())

我的问题是 我想分别从惩罚和晋升表中统计每个员工当年受到的惩罚和晋升的次数 我做了这个查询，但没有得到正确的结果

SELECT e.fullname , COUNT(punish.emp_id) as siza ,COUNT(pro.emp_id) as supas
  FROM emp_employee as e
  LEFT JOIN emp_punishment as punish on punish.emp_id=e.id
  LEFT JOIN emp_promotion as pro on e.id=pro.emp_id
 WHERE ((MONTH(e.promotionDate) = MONTH(CURRENT_DATE())
   AND YEAR(e.promotionDate) = YEAR(CURRENT_DATE()))
   AND ( YEAR(punish.directorate_date) = YEAR(CURRENT_DATE()) )
   AND ( YEAR(pro.directorate_date) = YEAR(CURRENT_DATE()) )
 GROUP BY e.fullname;

请帮忙。

Answer 1

通过直接连接 3 个表，您会得到重复的行。
按 emp_id 分组并分别聚合每个表 emp_punishment 和 emp_promotion 并将结果连接到表 emp_employee。

select e.fullname, coalesce(pu.siza, 0) siza, coalesce(pr.supas, 0) supas
from emp_employee as e 
left join (
  select emp_id, count(*) siza
  from emp_punishment
  where year(directorate_date) = year(CURRENT_DATE)
  group by emp_id
) pu on pu.emp_id = e.id
left join (
  select emp_id, count(*) supas
  from emp_promotion
  where year(directorate_date) = year(CURRENT_DATE)
  group by emp_id
) pr on pr.emp_id = e.id 

我只用了条件:

where year(directorate_date) = year(CURRENT_DATE())

因为在你的问题中你说:
我想统计每个员工在 当年 从惩罚和晋升中受到的惩罚和晋升