列出参与多个项目的员工姓名

Question

有两个与此相关的表。工作和员工。这两个表的内容是员工的 EMPID NAME SALARY DID（部门 ID）和 PID EMPID HOURS from work on。我写的SQL是

select e.name, w.pid
from employee e, workon w
where e.empid = w.empid
group by e.name, w.pid, w.empid
having count (e.name) > 1
order by w.pid

我一直试图弄清楚为什么这段代码不会给我提供从事多个项目的员工。请帮我弄清楚我做错了什么。

Answer 1

您的 group by 为每个项目的每位员工返回一行，根据定义，这永远不会超过 1 行

下面的sql应该可以工作

警告：我不确定这将如何影响服务器使用的性能，风险自负

以下将为每个员工每次工作返回 1 行，但仅限于具有超过 1 个工作记录的员工（因此，如果员工有 5 个工作记录，您将获得 5 行具有相同的 e.name 和 5 个不同的 w.pid 值)

select e.name, w.pid
from employee e, workon w
where e.empid = w.empid
and e.empid in (
select w.empid
from workon w -- there was a typo here originally
group by 1
having count (*) > 1
)
order by e.name, w.pid

Answer 2

SELECT E.NAME, W.PID
from employee e inner join workon w on e.empid = w.empid
where e.empid in (select EMPID from workon GROUP BY EMPID HAVING COUNT(EMPID) > 1)

子查询正在计算与该 empid 关联的所有记录与超过 1 个项目，并且主查询正在检查 empid 表中的 empid 是否在子查询的结果中。

Answer 3

您可以尝试以下查询。

在一个变量中，所有不同计数的部门都取自部门主表。之后，只有那些计数与关系表中的不同链接部门计数匹配的员工被选中。

CREATE TABLE employees
(
    employee_id int NOT NULL CONSTRAINT pk_employees PRIMARY KEY,
    employee_name nvarchar(128) NOT NULL CONSTRAINT uk_employees_employee_name UNIQUE
);

CREATE TABLE departments
(
    department_id int NOT NULL PRIMARY KEY,
    department_name nvarchar(128) NOT NULL CONSTRAINT uk_departments_department_name UNIQUE
);

CREATE TABLE department_employees
(
    department_id int NOT NULL CONSTRAINT fk_department_employees_departments REFERENCES departments(department_id),
    employee_id int NOT NULL CONSTRAINT fk_departement_employees_employees REFERENCES employees(employee_id),
    CONSTRAINT pk_deparment_employees PRIMARY KEY (department_id, employee_id)
)

INSERT INTO employees
VALUES (1, 'John Doe'), (2, 'Jane Doe'), (3, 'William Doe'), (4, 'Margaret Doe')

INSERT INTO departments
VALUES (1, 'Accounting'), (2, 'Humman Resources'), (3, 'Marketing')

INSERT INTO department_employees
VALUES 
    (1, 1), (2, 1), (3, 1), 
    (2, 2), (2, 3),
    (3, 3), (3, 4)

declare @distinctDeptCount int 
SET @DistinctDeptCount = (SELECT Count(Distinct department_id) FROM departments)
--SELECT @DistinctDeptCount

SELECT Distinct employees.employee_id, employee_name
from employees     
where employees.employee_id in (
select employee_id from department_employees GROUP BY employee_id HAVING COUNT(department_id) >= @distinctDeptCount
)

这是现场演示Emp. with all Department 输出如下图

employee_id employee_name
1           John Doe