listagg函数替代方案_listagg within group用法

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这是一个Oracle的列转行函数：LISTAGG()
注：oracle 11.2才能用

先看示例代码：

Sql代码 
1.with temp as(  
2.  select ‘China’ nation ,’Guangzhou’ city from dual union all 
3.  select ‘China’ nation ,’Shanghai’ city from dual union all 
4.  select ‘China’ nation ,’Beijing’ city from dual union all 
5.  select ‘USA’ nation ,’New York’ city from dual union all 
6.  select ‘USA’ nation ,’Bostom’ city from dual union all 
7.  select ‘Japan’ nation ,’Tokyo’ city from dual   
8.)  
9.select nation,listagg(city,’,’) within GROUP (order by city)  
10.from temp 
11.group by nation 
with temp as(
  select ‘China’ nation ,’Guangzhou’ city from dual union all
  select ‘China’ nation ,’Shanghai’ city from dual union all
  select ‘China’ nation ,’Beijing’ city from dual union all
  select ‘USA’ nation ,’New York’ city from dual union all
  select ‘USA’ nation ,’Bostom’ city from dual union all
  select ‘Japan’ nation ,’Tokyo’ city from dual
)
select nation,listagg(city,’,’) within GROUP (order by city)
from temp
group by nation 这是最基础的用法：

LISTAGG(XXX,XXX) WITHIN GROUP( ORDER BY XXX)

用法就像聚合函数一样，通过Group by语句，把每个Group的一个字段，拼接起来。

非常方便。

同样是聚合函数，还有一个高级用法：

就是over(partition by XXX)

也就是说，在你不实用Group by语句时候，也可以使用LISTAGG函数：

Sql代码 
1.with temp as(  
2.  select 500 population, ‘China’ nation ,’Guangzhou’ city from dual union all 
3.  select 1500 population, ‘China’ nation ,’Shanghai’ city from dual union all 
4.  select 500 population, ‘China’ nation ,’Beijing’ city from dual union all 
5.  select 1000 population, ‘USA’ nation ,’New York’ city from dual union all 
6.  select 500 population, ‘USA’ nation ,’Bostom’ city from dual union all 
7.  select 500 population, ‘Japan’ nation ,’Tokyo’ city from dual   
8.)  
9.select population,  
10.       nation,  
11.       city,  
12.       listagg(city,’,’) within GROUP (order by city) over (partition by nation) rank  
13.from temp 
with temp as(
  select 500 population, ‘China’ nation ,’Guangzhou’ city from dual union all
  select 1500 population, ‘China’ nation ,’Shanghai’ city from dual union all
  select 500 population, ‘China’ nation ,’Beijing’ city from dual union all
  select 1000 population, ‘USA’ nation ,’New York’ city from dual union all
  select 500 population, ‘USA’ nation ,’Bostom’ city from dual union all
  select 500 population, ‘Japan’ nation ,’Tokyo’ city from dual
)
select population,
       nation,
       city,
       listagg(city,’,’) within GROUP (order by city) over (partition by nation) rank
from temp

总结：LISTAGG()把它当作SUM()函数来使用就可以了。