Oracle行专列函数Listagg()和WMSYS.WM_CONCAT()

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WMSYS.WM_CONCAT: 依赖WMSYS 用户，不同oracle环境时可能用不了，返回类型为CLOB，可用substr截取长度后to_char转化为字符类型

LISTAGG : 11g2才提供的函数，不支持distinct,拼接长度不能大于4000,函数返回为varchar2类型，最大长度为4000.

WMSYS.WM_CONCAT()

select deptno,wmsys.wm_concat(ename) enames ,sum(sal) sal
from emp group by deptno;

Oracle行专列函数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
     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。

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