Mysql实现rank和sum over窗口函数示例

Mysql8.0以下版本是不支持窗口函数的，下面简单演示了mysql如何通过@变量实现rank和sum over窗口函数。各位读者可以以此举一反三。

数据准备：

CREATE TABLE sc (
  SId VARCHAR(10),
  CId VARCHAR(10),
  score INT
 );
 
 INSERT INTO sc (SId, CId, score)
 VALUES
  ('01', '01', 80),
  ('01', '02', 90),
  ('01', '03', 99),
  ('02', '01', 70),
  ('02', '02', 60),
  ('02', '03', 80),
  ('03', '01', 80),
  ('03', '02', 80),
  ('03', '03', 80),
  ('04', '01', 50),
  ('04', '02', 30),
  ('04', '03', 20),
  ('05', '01', 76),
  ('05', '03', 77);
 
 CREATE TABLE t_access_times (
  USER VARCHAR(10),
   DATE DATE,
   COUNT INT
 );
 
 INSERT INTO t_access_times (USER, DATE, COUNT)
 VALUES
  ('A', '2015-01-02', 5),
  ('A', '2015-01-03', 15),
  ('B', '2015-01-01', 5),
  ('A', '2015-01-04', 8),
  ('B', '2015-01-05', 25),
  ('A', '2015-01-06', 5),
  ('A', '2015-02-02', 4),
  ('A', '2015-02-06', 6),
  ('B', '2015-02-06', 10),
  ('B', '2015-02-07', 5);

实现rank

不分组全局排名

 SELECT s.*,@r :=@r + 1 AS rank
 FROM sc s,(SELECT @r := 0) r
 ORDER BY score DESC;

按照班级分组的每个学生成绩排名

 SELECT a.cid,a.sid,a.score,a.rank
 FROM  
 (
   SELECT s.*,
   IF(@p=cid,@r:=@r+1,@r:=1) AS rank,
   @p:=cid
   FROM sc s,(SELECT @p:=0,@r:=0)r
   ORDER BY cid,score DESC
 )a;

更多关于rank的示例可以参考：

分组排序求前三？TopN问题？一文教你MySQL各类排序操作

引用自：https://blog.csdn.net/weixin_41261833/article/details/103511400

实现sum over

全表累积求和

 SELECT t.*,@c :=@c + COUNT AS accumulate
 FROM t_access_times t,(SELECT @c := 0) c
 ORDER BY USER,DATE;

分组的累积求和

 SELECT a.user,a.date,a.count,a.accumulate
 FROM  
 (
   SELECT t.*,
   IF(@p=USER,@r:=@r+COUNT,@r:=COUNT) AS accumulate,
   @p:=USER
   FROM t_access_times t,(SELECT @p:=0,@c:=0)c
   ORDER BY USER,DATE
 )a;