MySQL5.7实现分组排序

文章目录

• 前言
• 一、准备数据
• 二、查询

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前言

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MySQL5.7版本没有row_number()over()函数，MySQL8以上版本才有，但是MySql5.7安装的版本较多，在5.7如何进行排序分组。

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一、准备数据

 CREATE TABLE POSTS(POST_ID INT,
				   USER_ID INT, -- 用户ID
				   CATEGORY_ID INT,-- 分类ID
				   POST_TITLE VARCHAR(400), 
				   CREATE_TIME DATE, -- 创建时间
				   LAST_EDIT_TIME DATE, -- 最后编辑时间
				   VIEW_COUNT INT,-- 访问量
				   REPLY_COUNT INT -- 回复量
				   );
				  
	
INSERT INTO POSTS(POST_ID,USER_ID,CATEGORY_ID,POST_TITLE,CREATE_TIME,LAST_EDIT_TIME,VIEW_COUNT,REPLY_COUNT)VALUES(1,1,1,'标题1',now(),now(),100,400);
INSERT INTO POSTS(POST_ID,USER_ID,CATEGORY_ID,POST_TITLE,CREATE_TIME,LAST_EDIT_TIME,VIEW_COUNT,REPLY_COUNT)VALUES(2,1,1,'标题2',now(),now(),200,300);
INSERT INTO POSTS(POST_ID,USER_ID,CATEGORY_ID,POST_TITLE,CREATE_TIME,LAST_EDIT_TIME,VIEW_COUNT,REPLY_COUNT)VALUES(3,2,1,'标题3',now(),now(),300,200);
INSERT INTO POSTS(POST_ID,USER_ID,CATEGORY_ID,POST_TITLE,CREATE_TIME,LAST_EDIT_TIME,VIEW_COUNT,REPLY_COUNT)VALUES(4,2,1,'标题4',now(),now(),400,100);
INSERT INTO POSTS(POST_ID,USER_ID,CATEGORY_ID,POST_TITLE,CREATE_TIME,LAST_EDIT_TIME,VIEW_COUNT,REPLY_COUNT)VALUES(5,2,1,'标题5',now(),now(),500,100);
INSERT INTO POSTS(POST_ID,USER_ID,CATEGORY_ID,POST_TITLE,CREATE_TIME,LAST_EDIT_TIME,VIEW_COUNT,REPLY_COUNT)VALUES(6,1,2,'标题4',now(),now(),600,100);
INSERT INTO POSTS(POST_ID,USER_ID,CATEGORY_ID,POST_TITLE,CREATE_TIME,LAST_EDIT_TIME,VIEW_COUNT,REPLY_COUNT)VALUES(7,2,2,'标题5',now(),now(),700,100);

二、查询

根据查询各个分类的访问量的排名

SELECT A.*,@last :=IF(@FIRST = A.CATEGORY_ID, @last + 1, 1 ) AS rn, @FIRST := A.CATEGORY_ID 
FROM POSTS A,(SELECT @last := 0, @FIRST := NULL ) B
ORDER BY A.CATEGORY_ID,VIEW_COUNT DESC;