Oracle 列转行函数 Listagg()

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最基础的用法：

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

例如有这样一张表：

FID FType FName

1 DB MySQL

1 DB Oracle

现在我们需要得到以下结果：

FID FType FName

1 DB MySQL,Oracle

这个查询结果其实很好实现，在Oracle 11g中为我们提供了Listagg函数，下面就是查询语句：

SELECT FID, FType,LISTAGG(FName, ‘,’) WITHIN GROUP (ORDER BY FName) AS FNameFROM TABLENAMEGROUP BY FID

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。

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

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

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