邻接模型MySQL语法

Question

我用邻接模型来表示一个孩子/父母的关系。

它被用来反映公司的等级制度，每个员工都有一名经理。员工和经理都存储在同一个表中，因此managerID字段引用特定经理的userID。

以下是我的表结构：userID -电子邮件-密码- firstName - lastName - officeID - departmentID - managerID - roleID -用户名

因此，managerID是一个外键，但来源于相同的模式。

我想要做的是显示一个包含系统用户的信息的表格--包括他们的经理。

到目前为止，我已经使用以下SQL语句使用多个联接实现了这一点：

SELECT user.firstName, user.lastName, office.officeName, department.departmentTitle, role.roleName
FROM user, office, department, role
WHERE user.officeID = office.officeID
AND user.departmentID = department.departmentID
AND user.roleID = role.roleID

然而，我不知道如何显示经理的名字。

任何帮助都将不胜感激。

Answer 1

您的查询只会吸引用户。要获得经理名称，您需要再次加入user表，如下所示：

SELECT u.firstName, u.lastName, 
       o.officeName, d.departmentTitle, 
       r.roleName, 
       m.firstName AS mFN, m.lastName AS mLN
FROM user u JOIN office o ON (u.officeID = o.officeID)
            JOIN department d ON (u.departmentID = d.departmentID)
            JOIN role r ON (u.roleID = r.roleID)
            JOIN user m ON (u.manager_id=m.user_id);

Answer 2

只需使用managerID=m.userID条件再次加入用户表

m.firstName和m.lastName是经理的名字

SELECT user.firstName, user.lastName, m.firstName,m.lastName, office.officeName, department.departmentTitle, role.roleName
FROM user as u, user as m, office, department, role
WHERE u.officeID = office.officeID
AND u.departmentID = department.departmentID
AND u.roleID = role.roleID
AND u.managerID=m.userID

Answer 3

如果每个用户都有一个管理器(而且managerID不是null)，那么您可以安全地将左连接更改为内部连接。

SELECT u.firstName
     , u.lastName
     , office.officeName
     , department.departmentTitle
     , role.roleName
     , manager.firstName AS managerFirstName
     , manager.lastName AS managerLastName
  FROM user AS u
    JOIN office
      ON u.officeID = office.officeID
    JOIN department
      ON u.departmentID = department.departmentID
    JOIN role
      ON u.roleID = role.roleID
    LEFT JOIN user AS manager
      ON u.managerID = manager.userID