MySQL 以及 Python 实现排名窗口函数_MySQL

python 大部分数据库都提供了窗口函数，比如RANK,ROW_NUMBER等等。 MySQL 这方面没有直接提供，但是可以变相的实现，我以前写了row_number 的实现，今天有时间把 rank 的实现贴出来。
这里，我用MySQL 以及Python 分别实现了rank 窗口函数。
原始表信息：

t_girl=# /d group_concat; Table "ytt.group_concat"Column| Type| Modifiers ----------+-----------------------+----------- rank | integer |username | character varying(20) |

表数据

t_girl=# select * from group_concat; rank | username ------+----------100 | Lucy127 | Lucy146 | Lucy137 | Lucy104 | Lucy121 | Lucy136 | Lily100 | Lily100 | Lily105 | Lily136 | Lily149 | ytt116 | ytt116 | ytt149 | ytt106 | ytt117 | ytt(17 rows)Time: 0.638 ms

PostgreSQL 的rank 窗口函数示例：

t_girl=# select username,rank,rank() over(partition by username order by rank desc) as rank_cnt from group_concat; username | rank | rank_cnt ----------+------+---------- Lily |136 |1 Lily |136 |1 Lily |105 |3 Lily |100 |4 Lily |100 |4 Lucy |146 |1 Lucy |137 |2 Lucy |127 |3 Lucy |121 |4 Lucy |104 |5 Lucy |100 |6 ytt|149 |1 ytt|149 |1 ytt|117 |3 ytt|116 |4 ytt|116 |4 ytt|106 |6(17 rows)Time: 131.150 ms

MySQL 提供了group_concat 聚合函数可以变相的实现：

mysql> select a.username, a.rank, find_in_set(a.rank,b.rank_gp) as rank_cnt from group_concat as a ,(select username,group_concat(rank order by rank desc separator ',')as rank_gp from group_concat group by username ) b where a.username = b.username order by a.username asc,a.rank desc;+----------+------+----------+| username | rank | rank_cnt |+----------+------+----------+| Lily |136 |1 || Lily |136 |1 || Lily |105 |3 || Lily |100 |4 || Lily |100 |4 || Lucy |146 |1 || Lucy |137 |2 || Lucy |127 |3 || Lucy |121 |4 || Lucy |104 |5 || Lucy |100 |6 || ytt|149 |1 || ytt|149 |1 || ytt|117 |3 || ytt|116 |4 || ytt|116 |4 || ytt|106 |6 |+----------+------+----------+17 rows in set (0.02 sec)

当然了，如果MySQL SQL不太熟悉，可以用程序来处理，比如我下面用python 实现了rank 函数，执行结果如下：（脚本源代码最后）

>>> ================================ RESTART ================================>>>username | rank | rank_cnt --------------------------------ytt |149 |1 ytt |149 |1 ytt |117 |3 ytt |116 |4 ytt |116 |4 ytt |106 |6 Lucy|146 |1 Lucy|137 |2 Lucy|127 |3 Lucy|121 |4 Lucy|104 |5 Lucy|100 |6 Lily|136 |1 Lily|136 |2 Lily|105 |3 Lily|100 |4 Lily|100 |4 (17 Rows.)Time: 0.162 Seconds.

附上脚本代码：

from __future__ import print_functionfrom datetime import date, datetime, timedeltaimport mysql.connectorimport time# Created by ytt 2014/5/14.# Rank function implement.def db_connect(is_true):	cnx = mysql.connector.connect(host='192.168.1.131',port='3306',user='python_user', password='python_user',database='t_girl',autocommit=is_true)	return cnxdef db_rs_rank(c1 ='username desc' ,c2 = ' rank desc'):	# c1: partition column.	# c2: sort column.	time_start = time.time()	cnx = db_connect(True)	rs = cnx.cursor()	query0 = "select username,rank from group_concat order by " + c1 + ", " + c2	rs.execute(query0,multi=False)	if rs.with_rows:		rows = rs.fetchall()	else:		return "No rows affected."	i = 0	j = 0	k = 1	result = []	field1_compare = rows[0][0]	field2_compare = rows[0][1]	while i