wm_concat 和listagg 函数都可以实现对（单个或组合）列的合并，也可以看成是对某一列的“SUM”，这俩个函数功能相同，listagg是在11.2的版本中才首次出现的，wm_concat在12c版本中被取消。
常见用法
select t.job,listagg(t.ename,’,’) within group(order by hiredate asc) from scott.emp t group by t.job;
select t.job,wm_concat(t.ename) from scott.emp t group by t.job;
–去重
with tb as(
select sys_guid() id,‘t1’ name, ‘CLERK’ job from dual
union select sys_guid() id,‘t1’ name, ‘SALESMAN’ job from dual
union select sys_guid() id,‘t1’ name, ‘MANAGER’ job from dual
union select sys_guid() id,‘t1’ name, ‘CLERK’ job from dual
union select sys_guid() id,‘t2’ name, ‘MANAGER’ job from dual
union select sys_guid() id,‘t2’ name, ‘MANAGER’ job from dual
)
select t.name, wm_concat(distinct t.job) jobs from tb t group by t.name;
对比
wm_cancat函数行转列后，不会按照原有查询结果排序。listagg函数行转列后，会按照原有查询结果顺序排列。如果考虑到需要行转列，并且保持分组后顺序不变可以使用listagg来完成。
wm_concat的使用（listagg上限varchar4000）
select dev_id,regexp_replace(regexp_replace(wm,’,’,’;’),’#’,’,’) coords from
(select dev_id ,wm_concat(t.x||’#’||t.y) over(partition by t.dev_id order by gps_time) wm ,
row_number() over(partition by dev_id order by gps_time desc) rm
from t_dev_loc t where t.dev_id in (‘37080000000034798’,‘37080000000034488’)
and gps_time between to_date(‘2018-11-05 00:00:00’,‘yyyy-mm-dd hh24:mi:ss’) and sysdate
)where rm=1;
行转列排序2( 突破listagg上限进行行转列排序)
with tb as(
select sys_guid() id,‘t1’ name, ‘CLERK’ job from dual
union select sys_guid() id,‘t1’ name, ‘SALESMAN’ job from dual
union select sys_guid() id,‘t1’ name, ‘MANAGER’ job from dual
union select sys_guid() id,‘t1’ name, ‘CLERK’ job from dual
union select sys_guid() id,‘t2’ name, ‘MANAGER’ job from dual
union select sys_guid() id,‘t2’ name, ‘MANAGER’ job from dual
)
– 突破listagg上限进行行转列排序
select t.name,
xmlagg(xmlparse(content t.job || ‘,’ wellformed) order by t.id asc)
.getclobval() jobs
from tb t
group by t.name
作者：clannad_
链接：https://www.jianshu.com/p/92cfd2f150f9
来源：简书
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