Oracle 列转行函数 Listagg()

本文来源于：dacoolbaby 的 <Oracle 列转行函数 Listagg()>

这是一个Oracle的列转行函数：LISTAGG()

  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

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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：

  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

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总结：LISTAGG()把它当作SUM()函数来使用就可以了。