Mysql實現rank和sum over窗口函數示例

Mysql8.0以下版本是不支持窗口函數的，下面簡單演示了mysql如何通過@變量實現rank和sum over窗口函數。各位讀者可以以此舉一反三。

數據準備：

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);

實現rank

不分組全局排名

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

按照班級分組的每個學生成績排名

 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;

更多關於rank的示例可以參考：

分組排序求前三？TopN問題？一文教你MySQL各類排序操作

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

實現sum over

全表累積求和

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

分組的累積求和

 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;