wm_concat的使用

with aa as(
select 1 a, 'a' b from dual union all
select 1, 'b' from dual union all
select 1, 'c' from dual union all
select 2, 'a' from dual union all
select 2, 'e' from dual union all
select 2, 'f' from dual )
select a,wm_concat(b) from aa
group by a;