Максим Y

with great_design_tab as (
  select 700 as id, '1,11,32,531' as ass_pain from dual union all
  select 701 as id, '2, 44, 321' as ass_pain from dual
)
,usrs as (
  select 1 as id, 'вася' as username from dual union all
  select 11 as id, 'петя' as username from dual union all
  select 32 as id, 'костя' as username from dual union all
  select 531 as id, 'дима' as username from dual union all
  select 2 as id, 'жора' as username from dual union all
  select 44 as id, 'изя' as username from dual union all
  select 321 as id, 'семен' as username from dual
)
select u.id, u.username, t.id
  from usrs u
      ,great_design_tab t
      ,lateral (
                select level x from dual 
                connect by regexp_substr(ass_pain, '[^,]+', 1, level) is not null
               )
 where u.id = trim(regexp_substr(ass_pain,'[^,]+', 1, x));

ID USERNAME         ID
---------- -------- ----------
         1 вася            700
        11 петя            700
        32 костя           700
       531 дима            700
         2 жора            701
        44 изя             701
       321 семен           701