PHP MySQL將用戶表連接到多個列和行

Question

對於我正在進行的項目中的項目，我一直有一些問題。

我有3個表，一個用於項目，一個用於客戶，一個用於用戶。 我正在嘗試在Projects表中存儲Customers和Users的ID，並在檢索時加入它們。

+----+--------------+
| ID | CustomerName |
+----+--------------+
|  1 | Customer 1   |
|  2 | Customer 2   |
|  3 | Customer 3   |
+----+--------------+

+----+-----------+----------+
| ID | FirstName | LastName |
+----+-----------+----------+
|  1 | Bob       | Belcher  |
|  2 | Stirling  | Archer   |
|  3 | Bart      | Simpson  |
|  4 | Peter     | Griffin  |
|  5 | BoJack    | Horseman |
|  6 | Eric      | Cartman  |
+----+-----------+----------+

+----+---------------+-----------------+-------------+-------------------+-------------------+--------------------+
| ID | ProjectNumber | ProjectCustomer | ProjectLead | ProjectElectrical | ProjectMechanical | ProjectDescription |
+----+---------------+-----------------+-------------+-------------------+-------------------+--------------------+
|  1 | 0001          |               1 |           3 |                 4 |                 6 | Project 1          |
|  2 | 0002          |               2 |           2 |                 5 |                 5 | Project 2          |
|  3 | 0003          |               3 |           1 |                 6 |                 4 | Project 3          |
+----+---------------+-----------------+-------------+-------------------+-------------------+--------------------+

我一整天都在玩Select，這就是我能夠搜索到的：

select Projects.ProjectNumber, Customers.CustomerName, CONCAT_WS(' ', Users.FirstName, Users.LastName) AS ProjectLead, Projects.ProjectElectrical, Projects.ProjectMechanical, Projects.ProjectDescription FROM Projects
INNER JOIN Customers ON Projects.ProjectCustomer = Customers.ID
LEFT JOIN Users ON Projects.ProjectLead = Users.ID

這讓我成為那里的一部分：

+---------------+--------------+-----------------+-------------------+-------------------+--------------------+
| ProjectNumber | CustomerName | ProjectLead     | ProjectElectrical | ProjectMechanical | ProjectDescription |
+---------------+--------------+-----------------+-------------------+-------------------+--------------------+
| 0001          | Customer 1   | Bart Simpson    |                 4 |                 6 | Project 1          |
| 0002          | Customer 2   | Stirling Archer |                 5 |                 5 | Project 2          |
| 0003          | Customer 3   | Bob Belcher     |                 6 |                 4 | Project 3          |
+---------------+--------------+-----------------+-------------------+-------------------+--------------------+

但對於我的生活，我不能讓ProjectElectrical和ProjectMechanical做與ProjectLead相同的事情。 我要么重復ProjectLead，要么得到NULL。

誰能幫助我指出正確的方向？ 我是否需要完全重新設計我的查詢，還是我在正確的軌道上？

我在SQL Fiddle上搞砸了它

在此先感謝所有回復！

Answer 1

這是來自小提琴的更新查詢：

select Projects.ProjectNumber, Customers.CustomerName, CONCAT_WS(' ', Users.FirstName, Users.LastName) AS ProjectLead, CONCAT_WS(' ', u2.FirstName, u2.LastName) AS ProjectElectrical, CONCAT_WS(' ', u3.FirstName, u3.LastName) AS ProjectMechanical, Projects.ProjectDescription FROM Projects
INNER JOIN Customers ON Projects.ProjectCustomer = Customers.ID
LEFT JOIN Users ON Projects.ProjectLead = Users.ID
LEFT JOIN Users AS u2 ON Projects.ProjectElectrical = u2.ID
LEFT JOIN Users AS u3 ON Projects.ProjectMechanical = u3.ID