复杂查询 - 检索在两个特定部门工作的员工

Question

我正在尝试找出一种方法来检索在两个不同部门工作的员工。

我有 3 个简单的表格：

员工（employee_id、employee_name）
部门（department_id、department_name）
工作（开斋节，做了，work_time）

所以我试着写了一个 SQL 查询：

 select employee_name
 from employee, working,department
 where eid = employee_id 
   and did = department_id 
   and department_name = 'software'
   and dname = 'hardware';

但是它不起作用，我的问题是什么？

Answer 1

您可以轻松获取在某一特定部门工作的员工：

select *
  from Employee e inner join
       Working w on e.employee_id = w.eid inner join
       Department d on w.did = d.department_id
 where d.name = 'software'

现在暧昧来了。如果你想让所有员工工作在 software 或在 hardware:

-- Employees who work at either software or hardware or both departments
select *
  from Employee e inner join
       Working w on e.employee_id = w.eid inner join
       Department d on w.did = d.department_id
 where d.name = in ('software', 'hardware')

如果你想获得在software和hardware部门工作的员工：

-- Employees who work in both hardware and software deparments simultaneously 
select *
  from Employee e inner join
       Working w on e.employee_id = w.eid inner join
       Department d on w.did = d.department_id
 where d.name = 'software'

intersect

select *
  from Employee e inner join
       Working w on e.employee_id = w.eid inner join
       Department d on w.did = d.department_id
 where d.name = 'hardware'

Answer 2

问题是您要求部门同时为 'software' 和 'hardware'。另外，dname 不是字段。

更正您的查询：

select employee_name
from employee, working, department
where eid = employee_id and did = department_id 
and (department_name = 'software' or department_name = 'hardware');

但我更喜欢这种查询：

SELECT DISTINCT e.employee_name
FROM employee e
JOIN working w ON w.eid = e.employee_id
JOIN department d ON d.department_id = w.did
WHERE d.department_name IN ('software', 'hardware');

也就是让员工在两个部门中的任何一个（或两个）工作。

如果您只想要同时在两个部门工作的员工，试试这个：

SELECT e.employee_id, e.employee_name
FROM employee e
JOIN working w ON w.eid = e.employee_id
JOIN department d ON d.department_id = w.did
WHERE d.department_name IN ('software', 'hardware')
GROUP BY e.employee_id HAVING COUNT(DISTINCT d.department_id) = 2;

Answer 3

What is my problem?

您的 table 中没有 dname 列。

您可以简化问题，因为您不需要 department table，因为 working table 包含 did 中的部门 ID列。

然后你需要 GROUP BY 每个员工并找到 HAVING 一个 COUNT 两个 DISTINCT 部门 ID：

SELECT MAX(e.employee_name)
FROM   employee e
       INNER JOIN working w
       ON e.employee_id = w.eid
GROUP BY e.employee_id
HAVING COUNT(DISTINCT w.did) = 2

如果您只想考虑 software 和 hardware 部门，那么：

SELECT MAX(e.employee_name)
FROM   employee e
       INNER JOIN working w
       ON e.employee_id = w.eid
       INNER JOIN department d
       ON w.did = d.department_id
WHERE  d.department_name IN ('software', 'hardware')
GROUP BY e.employee_id
HAVING COUNT(DISTINCT w.did) = 2

Answer 4

这样的事情对你有用吗？

SELECT
   count(*) as cnt,
   employee.employee_name
FROM
   employee
   JOIN working ON working.eid = employee.employee_id
   JOIN department ON department.department_id = working.did
WHERE
   department.department_name = 'software' or department.department_name = 'hardware'
GROUP BY employee.employee_name
HAVING cnt > 1

这将计算链接到软件或硬件部门的每位员工。或者您可以不使用 WHERE 子句，让所有员工在多个部门工作。

复杂查询 - 检索在两个特定部门工作的员工

Complex query - retrieve employees working in both two specific departments

sql

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