sql语句实现多列前缀匹配求比值
最近有一个需求，前缀匹配求比值，用sql语句实现起来比其他方法简单，所以就写了一个sql语句。如下：
数据库设计如下：
|fs_page_turn_multi_num_data | CREATE TABLE `fs_page_turn_multi_num_data` (
`day` int(11) default NULL,
`instance_id` int(11) default NULL,
`turn1ID` int(11) default NULL,
`turn2ID` int(11) default NULL,
`turn3ID` int(11) default NULL,
`turn4ID` int(11) default NULL,
`turn5ID` int(11) default NULL,
`num` int(11) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8
turn1ID不能为空，turn2ID到turn5ID都可以为空，且如果turnXID和turnYID，如果X<Y，则在turnYID不为空的情况下turnXID不为空。
如果数据表中存储数据如下：
a null null null null num1
a a null null null num2
a a a null null num3
a a a a null num4
a a a a a num5
则输出应该是：
a null null null null num1
a a null null null num2 rate1
a a a null null num3 rate2
a a a a null num4 rate3
a a a a a num5 rate4
且rate1=num2/num1 ，rate2=num3/num2 ............
SELECT t1.day,t1.instance_id,t1.turn1ID, t1.turn2ID, t1.turn3ID,t1.turn4ID,t1.turn5ID,
(CASE WHEN t2.num IS NULL OR t2.num=0 THEN 0 ELSE t1.num/t2.num END ) AS turn_rateFROM (
SELECT DAY,instance_id,turn1ID, turn2ID, turn3ID,turn4ID,turn5ID, num,
(CASE WHEN turn1ID IS NULL THEN 1 ELSE 0 END)+
(CASE WHEN turn2ID IS NULL THEN 1 ELSE 0 END)+
(CASE WHEN turn3ID IS NULL THEN 1 ELSE 0 END)+
(CASE WHEN turn4ID IS NULL THEN 1 ELSE 0 END)+
(CASE WHEN turn5ID IS NULL THEN 1 ELSE 0 END) AS null_num,
CONCAT(CONCAT_WS(',',turn1ID, turn2ID, turn3ID,turn4ID,turn5ID),',') AS con_ws
FROM `fs_page_turn_multi_num_data` WHERE DAY=day) t1 LEFT JOIN
(
SELECT DAY,instance_id,turn1ID, turn2ID, turn3ID,turn4ID,turn5ID, num,
(CASE WHEN turn1ID IS NULL THEN 1 ELSE 0 END)+
(CASE WHEN turn2ID IS NULL THEN 1 ELSE 0 END)+
(CASE WHEN turn3ID IS NULL THEN 1 ELSE 0 END)+
(CASE WHEN turn4ID IS NULL THEN 1 ELSE 0 END)+
(CASE WHEN turn5ID IS NULL THEN 1 ELSE 0 END) AS null_num,
CONCAT(CONCAT_WS(',',turn1ID, turn2ID, turn3ID,turn4ID,turn5ID),',') AS con_ws
FROM `fs_page_turn_multi_num_data` WHERE DAY=day) t2
ON t1.null_num=t2.null_num-1
AND t1.con_ws LIKE CONCAT(t2.con_ws,'%')