Question

如何根据参与建筑项目的员工人数自动获得每位员工的收入金额。已经尝试过这个，但错误。子查询返回超过1行。

SELECT e.name,
( SELECT( p.costs / count(r.employee_id)) 
FROM relation_employee r GROUP BY r.project_id ) AS revenue
FROM project p 
INNER JOIN relation_employee r ON p.id = r.project_id
INNER JOIN employee e ON r.employee_id = e.id

表员工
id INT
名称VARCHAR
表项目
id INT
名称VARCHAR
费用INT
table relation_employee
employee_id INT
project_id INT

Answer 1

不是在选择部分中使用相关子查询，而是可以将每个项目的员工数量作为要在from部分中使用的派生表获取，这对我来说至少看起来更清晰一些。查询可能如下所示：

-- revenue per employee
SELECT e.name, sum(p.costs * 1.0 / emp_count) AS revenue
FROM project p 
INNER JOIN relation_employee r ON p.id = r.project_id
INNER JOIN (SELECT project_id, count(employee_id) emp_count FROM relation_employee GROUP BY project_id) c ON c.project_id = p.id 
INNER JOIN employee e ON r.employee_id = e.id
GROUP BY e.name;

-- revenue per employee and project
SELECT 
  e.name as employee_name, 
  p.name as project_name, 
  sum(p.costs / emp_count) AS revenue
FROM project p 
INNER JOIN relation_employee r ON p.id = r.project_id
INNER JOIN (SELECT project_id, count(employee_id) emp_count FROM relation_employee GROUP BY project_id) c ON c.project_id = p.id 
INNER JOIN employee e ON r.employee_id = e.id
GROUP BY e.name, p.name;

Sample SQL Fiddle

MySQL - 关系的算术运算

1 个答案: