Question

所以我有一张员工表：

我正在尝试创建一个显示该员工所有信息的查询，但我对Employee_Reports_To位有点困惑。我想要出现的是存储在此列中的Employee_ID的First_Name和Last_Name（例如，Joe Bloggs ID 1，向员工Joanne Blog ID 50报告）

这需要加入还是只需要一个简单的选择。当我尝试时，数据库出现链接问题..

SELECT employee.*, departments.Department_Name, 
            jobTitle.Job_Title,
            (SELECT manager.First_Name, manager.Last_Name
                FROM Employee manager
                INNER JOIN employee AS employeeReportsTo
          ON manager.Employee_Reports_To = manager.Employee_ID   
            ) AS Reports_To
            FROM Employee employee
            LEFT JOIN Departments AS departments
                ON departments.Departments_ID = employee.Departments_ID
            LEFT JOIN Job_Title AS jobTitle
                ON jobTitle.Job_Title_ID = employee.Job_Title_ID
             ORDER BY `employee`.`Record_Active` DESC,
                     `employee`.`First_Name` ASC

任何帮助都将不胜感激！

Answer 1

试试这个解决方案：

SELECT emp.*,
       manager.First_Name, 
       manager.Last_Name,
       departments.Department_Name, 
       jobTitle.Job_Title
FROM Employee emp
INNER JOIN Employee manager
ON emp.Employee_Reports_To = manager.Employee_ID
LEFT JOIN Departments AS departments
ON departments.Departments_ID = emp.Departments_ID
LEFT JOIN Job_Title AS jobTitle
ON jobTitle.Job_Title_ID = emp.Job_Title_ID
ORDER BY emp.Record_Active DESC,
             emp.First_Name ASC

最好使用Join而不是Sub Query。

<强>编辑：

由于列Employee_Reports_To可以是null，因此最好使用LEFT JOIN代替INNER JOIN。像这样：

SELECT emp.*,
           manager.First_Name, 
           manager.Last_Name,
           departments.Department_Name, 
           jobTitle.Job_Title
FROM Employee emp
LEFT JOIN Employee manager                     --Changed Join here
ON emp.Employee_Reports_To = manager.Employee_ID
LEFT JOIN Departments AS departments
ON departments.Departments_ID = emp.Departments_ID
LEFT JOIN Job_Title AS jobTitle
ON jobTitle.Job_Title_ID = emp.Job_Title_ID
ORDER BY emp.Record_Active DESC,
         emp.First_Name ASC

Answer 2

查看您的代码，您可以使用两次Employee（别名为e1和e2）一个用于员工，一个用于相关经理

SELECT e1.*
  , departments.Department_Name
  , jobTitle.Job_Title
  , e2.First_Name
  ,e2.Last_Name
  FROM Employee e1
  INNER JOIN Employee e2 ON e1.Employee_Reports_To = e2.Employee_ID
  LEFT JOIN Departments AS departments
      ON departments.Departments_ID = e1.Departments_ID
  LEFT JOIN Job_Title AS jobTitle
      ON jobTitle.Job_Title_ID = e1.Job_Title_ID
   ORDER BY e1.`Record_Active` DESC,
           e1.`First_Name` ASC

子查询加入同一个表

2 个答案: