oracle sql语句问题，帮忙看一下，谢谢了！！！

Question

                 CASE
                  WHEN (select capgrade
                          from tb_tpost_userpost
                         where mpostid = i.mpostid
                           and spostid = i.spostid
                           and idcard = r.idcard) = 1 THEN
                   'Ⅰ级'
                  WHEN (select capgrade
                          from tb_tpost_userpost
                         where mpostid = i.mpostid
                           and spostid = i.spostid
                           and idcard = r.idcard) = 2 THEN
                   'Ⅱ级'
                  WHEN (select capgrade
                          from tb_tpost_userpost
                         where mpostid = i.mpostid
                           and spostid = i.spostid
                           and idcard = r.idcard) = 3 THEN
                   'Ⅲ级'
                  WHEN (select capgrade
                          from tb_tpost_userpost
                         where mpostid = i.mpostid
                           and spostid = i.spostid
                           and idcard = r.idcard) = 4 THEN
                   'Ⅳ级'
                  WHEN (select capgrade
                          from tb_tpost_userpost
                         where mpostid = i.mpostid
                           and spostid = i.spostid
                           and idcard = r.idcard) = 5 THEN
                   'Ⅴ级'
                  ELSE
                   '尚无等级'
                END usercapgrade 

语句太过长了，这个怎么改成外层嵌套一次查询，大佬帮忙看一下，谢谢

Answer 1

为什么写成这样？不知道是不是你想要的
select case when capgrade=1 then 'I级' when capgrade=2 then 'II级' when …… else '尚无等级' end usercapgrade
from tb_tpost_userpost
where mpostid = i.mpostid
and spostid = i.spostid
and idcard = r.idcard