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 | Lucy 127 | Lucy 146 | Lucy 137 | Lucy 104 | Lucy 121 | Lucy 136 | Lily 100 | Lily 100 | Lily 105 | Lily 136 | Lily 149 | ytt 116 | ytt 116 | ytt 149 | ytt 106 | ytt 117 | 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_cntfrom group_concat as a ,(select username,group_concat(rank order by rank desc separator ',') as rank_gp from group_concat group by username) bwhere 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 < len(rows): if field1_compare == rows[i][0]: j += 1 if field2_compare != rows[i][1]: field2_compare =rows[i][1] k = j result.append((rows[i][0],rows[i][1],k)) else: j = 1 k = 1 field1_compare = rows[i][0] result.append((rows[i][0],rows[i][1],k)) i += 1 i = 0 rows_header = list(rs.column_names) rows_header.append('rank_cnt') print (rows_header[0].center(10,' ') + '|' + rows_header[1].center(10,' ') + '|' + rows_header[2].center(10,' ')) print ('-'.center(32,'-')) while i < len(result): print (result[i][0].ljust(10,' ') + '|' + str(result[i][1]).ljust(10,' ') + '|' + str(result[i][2]).ljust(10,' ')) i += 1 rs.close() cnx.close() time_end = time.time() print ('(' + str(len(rows))+ ' Rows.)') print ("Time:" + str(round((time_end-time_start),3)).rjust(10,' ') + ' Seconds.') if __name__=='__main__': db_rs_rank()