Oracle Join

Question

TableA
hierarchy_id Child_level parent_level
1      4 null
1      3 4
1 2 3
TableB
Enitity_id level
1 4
1 3
1 2
1 1
Tablec
level level_type
1     1
2     2
3     2
4     3
Tabled
Entity_id Hierarchy_id
1          1
2          2
From the above tables i have to build a query that returns
Entity_id Hierarchy_id Child_level parent_level
1          1      4 null
1          1      3 4
1          1 2 3
1          null     1 null
How can i achieve this, the main problem i am facing is getting the child level '1' of type '1' in the result set,
as it is not linked to a hierarchy id.
Please suggest.

Answer 1

Hi,
Not knowing exactly what you mean, prerequisites are quite vague, but i should use a union.
What about this?
select d.entity_id, a.hierarchy_id, a.child_level, a.parent_level
  from tabled d, tablea a
where d.HIERARCHY_ID = a.HIERARCHY_ID
union
select d.entity_id, NULL, b.e_level, NULL
  from tabled d, tableb b
where d.entity_id = b.ENTITY_ID
   and not exists (select 'dummy'
                     from tablea a
                    where a.CHILD_LEVEL = b.E_LEVEL)
order by 1, 2 , 3 desc
ENTITY_ID HIERARCHY_ID CHILD_LEVEL PARENT_LEVEL
         1            1           4
         1            1           3            4
         1            1           2            3
         1                        1
SQL> Kind regards
Auke Quist