（010）每日SQL学习：按字母顺序排列字符串

需求：一串字母'ADFGH',需要按照顺序来显示：A D F G H

第一步：先把字符串拆分

with test as(
select 'ADFGH' as a from dual
)
select a ,substr(a,level,1)
from test
connect by level<=length(a)

第二步：用listagg拼接

with test as(
select 'ADFGH' as a from dual
)
select a ,(select listagg(substr(a,level,1),',') witnin group (order by substr(a,level,1))
from dual
connect by level<=length(a)) b
from test