MySQL 慢速分组查询

Question

我有6张 table 1. 产品介绍2. 属性一3.产品和属性pa(ID、pID、aID)4、公司c5. 用户 u6. 公司和用户cu(ID、cID、uID)

现在在管理中我想查看公司产品及其属性。

SELECT p.ID, p.name
from  products p
LEFT JOIN Product and Attribute pa  ON pa.pID =  p.ID 
LEFT JOIN Attributes a  ON a.pID =  pa.aID
LEFT JOIN Company and User cu  ON cu.UiD  = p.uID    AND cu.cID = 121 (spcific company id) 
WHERE 1 
GROUP BY p.ID

Answer 1

在 MySQL , GROUP BY 意味着 ORDER BY

如果不需要特定顺序，请添加ORDER BY NULL

By default, MySQL sorts all GROUP BY col1, col2, ... queries as if you specified ORDER BY col1, col2, ... in the query as well. If you include an ORDER BY clause explicitly that contains the same column list, MySQL optimizes it away without any speed penalty, although the sorting still occurs. If a query includes GROUP BY but you want to avoid the overhead of sorting the result, you can suppress sorting by specifying ORDER BY NULL. For example: