Question

我有3个表：项目，员工和 project_employee

雇员

ID（int，PK）
名称

项目

project_id（int，PK）
PROJECT_NAME

project_employee

project_id（int，PK）
employee_id（int，PK）

我要做的是编写一个查询，获取项目中没有的所有员工的ID和名称，例如项目编号9.

所以我试过了：

SELECT ID, Name 
FROM [employee], [project_employee] 
WHERE [employee].ID != [project_employee].emp_id AND [project_employee].project_id = 9;

但我总是得到空洞的结果，我的逻辑肯定有问题吗？

Answer 1

相反，尝试这样的事情，它应该让所有不属于project_id = 9

的用户

SELECT u.ID, u.Name 
FROM [User] u
WHERE u.ID NOT IN (SELECT pe.employee_id
                  FROM [project_employee] pe
                  WHERE pe.project_id = 9);

Answer 2

您可以使用LEFT JOIN获取所需数据

select e.id,e.name
from employee e
left join project_employee pe
on e.id = pe.employee_id
left join projects p
on pe.project_id = p.project_id
where p.project_id is null

（或）刚刚与project_employee表保持联系。假设没有项目的所有员工都是期望的输出，则没有检查任何条件。

select e.id,e.name
from employee e
left join project_employee pe
on e.id = pe.employee_id
where pe.project_id is null

Answer 3

SELECT ID, NAME 
FROM employee e
LEFT JOIN project_employee pe
    ON pe.employee_id = e.id
      AND pe.project_id = 9
WHERE pe.employee_id IS NULL

您甚至不需要项目表，因为您没有在项目中寻找员工。

Answer 4

您可以使用NOT EXISTS执行此操作：

SELECT u.ID, u.Name 
FROM [User] u
WHERE NOT EXISTS ( SELECT *
                   FROM [project_employee] pe
                   WHERE pe.project_id = 9 
                     AND pe.employee_id = u.ID);

Answer 5

他要求检查员工是否在特定项目中。不在解决方案中没问题，但我通常更喜欢使用左连接。

SELECT ID, NAME 
FROM employee e
LEFT JOIN project_employee pe
  ON pe.emp_id = e.id
  and pe.project_id = 9
WHERE pe.employee_id IS NULL

SQL Server：从多个表中选择查询

5 个答案: