这是一个Oracle的列转行函数：LISTAGG()
先看示例代码：
- 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
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：
- 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。
Oracle 列转行函数 Listagg()
原文：http://www.cnblogs.com/hugo-wangfeng/p/5049322.html
