listagg函数的用法

这是一个Oracle的列转行函数：LISTAGG()

先看示例代码：

Sql代码

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

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这是最基础的用法：

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

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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

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

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总结：LISTAGG()把它当作SUM()函数来使用就可以了。

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