使用橋接器連接表

Question

我需要MySQL的幫助。 Db給了我，不幸的是我無法以任何方式改變它的結構。

我需要提取屬於特定組的員工列表（例如group_id = 2）。我不擅長使用橋接來連接多個表。你能幫我一把嗎？

+---------------+ 
|employees  | 
+---------------+ 
|employee_id | 
|FirstName  | 
|LastName  | 
+---------------+ 

+-------------------------------+ 
|employees_department   | 
+-------------------------------+ 
|employee_id     | 
|department_id     | 
+-------------------------------+ 

+--------------+ 
|departments | 
+--------------+ 
|deparmtent_id | 
|name   | 
+--------------+ 

+--------------------------------+ 
|department_groups    | 
+--------------------------------+ 
|group_id      | 
|department_id     | 
+--------------------------------+ 

+---------------+ 
|groups   | 
+---------------+ 
|group_id  | 
|group_name  | 
+---------------+ 

我感謝您的幫助。

Answer 1

SELECT e.FirstName, e.LastName  
FROM department_groups AS dg 
JOIN employees_department AS ed ON (ed.department_id = dg.department_id) 
JOIN employees AS e ON (e.employee_id = ed.employee_id) 
WHERE dg.group_id = 2 

Answer 2

這個查詢應該做的伎倆：select * from employees, employees_department, department_groups, groups WHERE employees.employee_id = employees_department.employee_id and employees_department.department_id = department_groups.department_id and department_groups.group_id = groups.group_id and groups.group_id = 2

注意，如果GROUP_ID不是整數，這將失敗。相反，您可能必須更改最後一位groups.group_id = '2'。