Oracle 列转行函数 Listagg()

以下转自：http://dacoolbaby.iteye.com/blog/1698957  作者： dacoolbaby

这是一个Oracle的列转行函数：LISTAGG()

先看示例代码：

withtempas(
select'China' nation ,'Guangzhou' city from dual unionall
select'China' nation ,'Shanghai' city from dual unionall
select'China' nation ,'Beijing' city from dual unionall
select'USA' nation ,'New York' city from dual unionall
select'USA' nation ,'Bostom' city from dual unionall
select'Japan' nation ,'Tokyo' city from dual
)
select nation,listagg(city,',') within GROUP (orderby city)
fromtemp
groupby 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：

withtempas(
select 500 population, 'China' nation ,'Guangzhou' city from dual unionall
select 1500 population, 'China' nation ,'Shanghai' city from dual unionall
select 500 population, 'China' nation ,'Beijing' city from dual unionall
select 1000 population, 'USA' nation ,'New York' city from dual unionall
select 500 population, 'USA' nation ,'Bostom' city from dual unionall
select 500 population, 'Japan' nation ,'Tokyo' city from dual
)
select population,
       nation,
       city,
       listagg(city,',') within GROUP (orderby city) over (partition by nation) rank
fromtemp

总结：LISTAGG()把它当作SUM()函数来使用就可以了。