LEFT OUTER JOIN查詢不返回預期的行

Question

我的目標是使用第四個維恩圖來完成LEFT OUTER JOIN打算做的事情： SQL Diagrams ：

我的查詢根本沒有返回任何值，實際上，它應該返回Consultant_Memberships中的所有值減去Consultant_Memberships_Lists中存儲的值。

請參閱SQL Fiddle以便更容易理解：

SELECT * 
FROM   consultant_memberships 
       LEFT OUTER JOIN consultant_memberships_list 
                    ON consultant_memberships.`id` = 
                       consultant_memberships_list.membership_id 
WHERE  consultant_memberships_list.consultant_id = $id 
       AND consultant_memberships_list.membership_id IS NULL 

查詢使用'5'作為ID用於演示目的，以嘗試挑選正確的行。

Answer 1

由於WHERE子句上的consultant_id = 5 ，您當前的查詢基本上是在進行INNER JOIN 。 我相信你真的想用：

SELECT * 
FROM   consultant_memberships m
LEFT OUTER JOIN consultant_memberships_list l
  ON m.`id` = l.membership_id 
  AND l.consultant_id = 5 
WHERE l.membership_id IS NULL;

請參閱SQL Fiddle with Demo

Answer 2

使用

SELECT * 
   FROM   consultant_memberships 
       LEFT  Outer JOIN consultant_memberships_list 
                ON consultant_memberships_list.membership_id = consultant_memberships.`id`  
                and  consultant_memberships_list.consultant_id = 5 
 where  consultant_memberships_list.membership_id IS NULL;

在查詢“consultant_memberships_list.consultant_id = 5”之前使用的Where子句忽略了左外連接。