时间:2021-07-01 10:21:17 帮助过:38人阅读
p由于很多业务表因为历史原因或者性能原因,都使用了违反第一范式的设计模式。即同一个列中存储了多个属性值(具体结构见下表)。/pp这种模式下,应用常常需要将这个列依据分隔符进行分割,并得到列转行的结果。/p span class=cnblogs_code_copy/spanp style
由于很多业务表因为历史原因或者性能原因,都使用了违反第一范式的设计模式。即同一个列中存储了多个属性值(具体结构见下表)。
这种模式下,应用常常需要将这个列依据分隔符进行分割,并得到列转行的结果。
表数据:
ID | Value |
1 | tiny,small,big |
2 | small,medium |
3 | tiny,big |
期望得到结果:
ID | Value |
1 | tiny |
1 | small |
1 | big |
2 | small |
2 | medium |
3 | tiny |
3 | big |
#需要处理的表 create table tbl_name (ID int ,mSize varchar(100)); insert into tbl_name values (1,'tiny,small,big'); insert into tbl_name values (2,'small,medium'); insert into tbl_name values (3,'tiny,big'); #用于循环的自增表 create table incre_table (AutoIncreID int); insert into incre_table values (1); insert into incre_table values (2); insert into incre_table values (3);
select a.ID,substring_index(substring_index(a.mSize,',',b.AutoIncreID),',',-1) from tbl_name a join incre_table b on b.AutoIncreID <= (length(a.mSize) - length(replace(a.mSize,',',''))+1) order by a.ID;
这个join最基本原理是笛卡尔积。通过这个方式来实现循环。
以下是具体问题分析:
length(a.Size) - length(replace(a.mSize,',',''))+1 表示了,按照逗号分割后,改列拥有的数值数量,下面简称n
select a.ID,substring_index(substring_index(a.mSize,',',b.AutoIncreID),',',-1) from tbl_name a join incre_table b on b.AutoIncreID <= (length(a.mSize) - length(replace(a.mSize,',',''))+1) order by a.ID;
这个join最基本原理是笛卡尔积。通过这个方式来实现循环。
以下是具体问题分析:
length(a.Size) - length(replace(a.mSize,',',''))+1 表示了,按照逗号分割后,改列拥有的数值数量,下面简称n
join过程的伪代码:
根据ID进行循环
{
判断:i 是否 <= n
{
获取最靠近第 i 个逗号之前的数据, 即 substring_index(substring_index(a.mSize,',',b.ID),',',-1)
i = i +1
}
ID = ID +1
}
这种方法的缺点在于,我们需要一个拥有连续数列的独立表(这里是incre_table)。并且连续数列的最大值一定要大于符合分割的值的个数。
例如有一行的mSize 有100个逗号分割的值,那么我们的incre_table 就需要有至少100个连续行。
当然,mysql内部也有现成的连续数列表可用。如mysql.help_topic: help_topic_id 共有504个数值,一般能满足于大部分需求了。
改写后如下:
select a.ID,substring_index(substring_index(a.mSize,',',b.help_topic_id+1),',',-1) from tbl_name a join mysql.help_topic b on b.help_topic_id < (length(a.mSize) - length(replace(a.mSize,',',''))+1) order by a.ID;测试实例:
-- SELECT help_topic_id FROM mysql.help_topic -- eg.把一个字段用“,”分隔开组合 select group_concat(user_id ORDER BY user_id ASC) as nids from admin_user SELECT b.did,GROUP_CONCAT(b.sid ORDER BY adjustment DESC,similar DESC) FROM test b GROUP BY b.did -- 1.如果多个导购同1张单的先分解 -- 加时间段 select a.DJBH,a.je,substring_index(substring_index(a.dgy_list_id,',',b.help_topic_id+1),',',-1) from ipos_qtlsd a join mysql.help_topic b on b.help_topic_id < (length(a.dgy_list_id) - length(replace(a.dgy_list_id,',',''))+1) and a.djbh='BP0102_qtsy000070' order by a.DJBH; -- 2.取平均值 -- SELECT help_topic_id FROM mysql.help_topic -- 1.如果多个导购同1张单的先分解 -- @zddm -- @ rq select a.DJBH, substring_index(substring_index(a.dgy_list_id,',',b.help_topic_id+1),',',-1) AS FJID, substring_index(substring_index(a.dgy_list_mc,',',b.help_topic_id+1),',',-1) AS FJMC, FORMAT(a.je/(length(a.dgy_list_id) - length(replace(a.dgy_list_id,',',''))+1),2) AS FJJE, je from ipos_qtlsd a join mysql.help_topic b on b.help_topic_id < (length(a.dgy_list_id) - length(replace(a.dgy_list_id,',',''))+1) and a.rq BETWEEN UNIX_TIMESTAMP('2016-04-01') and UNIX_TIMESTAMP('2016-05-01') and a.djbh='gd_151125000001' order by a.DJBH; -- gd_151125000001 --3.分解后的指标 -- SELECT help_topic_id FROM mysql.help_topic -- 1.如果多个导购同1张单的先分解 -- @khdm_change 终端代码 -- @start_time 开始时间 -- @end_time 结束时间 -- SELECT * FROM ipos_qtlsd WHERE djbh='gd_151125000001' set @khdm_change ='BP0102'; set @start_time=UNIX_TIMESTAMP('2016-04-01'); set @end_time=UNIX_TIMESTAMP('2016-05-01'); SELECT FJID,FJMC,SUM(FJJE) FROM( select a.zddm,a.zdmc,a.DJBH, substring_index(substring_index(a.dgy_list_id,',',b.help_topic_id+1),',',-1) AS FJID, substring_index(substring_index(a.dgy_list_mc,',',b.help_topic_id+1),',',-1) AS FJMC, FORMAT(a.je/(length(a.dgy_list_id) - length(replace(a.dgy_list_id,',',''))+1),2) AS FJJE, je from ipos_qtlsd a join mysql.help_topic b on b.help_topic_id < (length(a.dgy_list_id) - length(replace(a.dgy_list_id,',',''))+1) and a.rq BETWEEN @start_time and @end_time and a.zd_id=(SELECT id from com_base_kehu where khdm=@khdm_change) ) AA GROUP BY FJID,FJMC -- and a.djbh='gd_151125000001' -- order by a.DJBH;