多表级联，实现功能强大，标题所不能描述，下面有图片

表brand0:

 

表brand1:

 

想要结合表brand0和表brand1，得到如下结果：

 

解决办法：

法1、

SELECT brand0.brand_id ,brand0.clickCount,brand1.saleCount FROM brand0 LEFT JOIN  brand1 
 ON  brand0.brand_id=brand1.brand_id UNION SELECT brand1.brand_id  ,brand0.clickCount,brand1.saleCount FROM brand0 RIGHT JOIN brand1 
ON  brand1.brand_id=brand0.brand_id

法2（推荐使用这种，容易）、

SELECT brand_id, SUM(clickCount) AS clickCount, SUM(saleCount ) AS saleCount FROM (  SELECT brand_id,clickCount, 0 saleCount FROM brand0 UNION ALL SELECT brand_id,0 clickCount, saleCount FROM brand1) ta GROUP BY ta.brand_id