php - 对不同表上的列求和并乘以另一个表上的列的值

Question

我需要根据参加的 session 、扣除额和发放的奖金来计算员工的月薪； 员工根据其职位的不同，每次 session 的薪酬也不同。

解决办法是: 工资=(每分钟工资* session 参加人数)+奖金-扣除额；

我有四张 table :

职位: ID、职位、pay_per_meeting

员工: ID、姓名、job_id

奖金: ID、金额、员工 ID、日期

扣除额: ID、金额、employee_id、日期

session : ID、employee_id、日期

SELECT
COUNT(meetings.employee_id) as meetings_attended, 
COUNT(deductions.amount) as debt, 
COUNT(bonuses.amount) bonus, 
(SELECT jobs.pay_per_attendance from jobs where jobs.id = (select job_id from employees where id=meetings.employee_id)) as pay,
((meetings_attended * pay) + bonus - debt) as salary 
FROM meetings 
JOIN deductions ON deductions.employee_id = meetings.employee_id 
JOIN bonuses ON bonuses.employee_id = meetings.employee_id 
WHERE meetings.employee_id = 1 
GROUP BY MONTH(meetings.date), MONTH(deductions.date), MONTH(bonuses.date)

每当我删除工资行时，上述查询都会返回许多不正确的值，但会给出未知列工资、meetings_attended、债务和奖金的错误，我确信分组有问题，但我不能只看到它。

Answer 1

您无法在定义的同一选择列表中引用列别名，您需要引用基础列。并且子查询无法访问主查询中计算的聚合。您需要重复聚合表达式，或者将所有内容移动到子查询中并在外部查询中使用它进行计算。

还有，你所有的COUNT()表达式将返回相同的结果，因为它们只是计算行数(我假设没有一个值可以是 NULL )。您可能想要COUNT(DISTINCT <column>)要获得不同的计数，您需要使用唯一的列，因此它们应该是主键列，例如COUNT(DISTINCT deductions.id) .

另一个问题是，当您在有多个联接时尝试对值进行求和和计数时，最终会得到过高的结果，因为行在所有表的叉积中出现重复。请参阅Join tables with SUM issue in MYSQL 。解决方案是计算子查询中每个表的总和。

SELECT m.month, m.meetings_attended, d.debt, b.bonus, 
    m.meetings_attended * j.pay_per_meeting + b.amount - d.amount AS salary
FROM (
    SELECT MONTH(date) AS month, COUNT(*) AS meetings_attended
    FROM meetings
    WHERE employee_id = 1
    GROUP BY month) AS m
JOIN (
    SELECT MONTH(date) AS month, COUNT(*) AS bonus, SUM(amount) AS amount
    FROM bonuses
    WHERE employee_id = 1
    GROUP BY month) AS b ON m.month = b.month
JOIN (
    SELECT MONTH(date) AS month, COUNT(*) AS debt, SUM(amount) AS amount
    FROM deductions
    WHERE employee_id = 1
    GROUP BY month) AS d ON m.month = d.month
CROSS JOIN employees AS e
JOIN jobs AS j ON j.id = e.job_id
WHERE e.employee_id = 1