2019獨角獸企業重金招聘Python工程師標準>>>

需求：

查詢出每個人2018年收藏量最高的專題資訊和專題數量

select t1.creatorId as puid,t1.course_Id,t1.`name`,resSubCount as 收藏量,MAX(t2.resSubCount) 
from mooc_subject t1 
	join mooc_subject_subscribeinfo t2 on t2.courseId =CONCAT(t1.course_Id)  
where published = 1 and status = 0 and createtime > '2018-01-01 00:00:00' and t2.cataid = 100000001 
GROUP BY t1.creatorId;
 

雖然也可以查詢出最大resSubCount，但是數值和其他自動根本對應不上，因為group by返回分組後的組內第一條資料資訊，max函式對應的是最大數量。

解決方法：

（）括號內的sql按resSubCount DESC排序，外層sql分組得到第一條資料，即為最大數量資料，問題解決

select * from (select t1.creatorId as puid,t1.course_Id,t1.`name`,resSubCount as 收藏量 from mooc_subject t1 
	join mooc_subject_subscribeinfo t2 on t2.courseId =CONCAT(t1.course_Id)  
where published = 1 and status = 0 and createtime > '2018-01-01 00:00:00' and t2.cataid = 100000001 
ORDER BY t2.resSubCount DESC) as b 
GROUP BY b.puid;
 

轉載於:https://my.oschina.net/kdy1994/blog/2906917