SQL Query Assistance Required for Full Outer Join

Question

Hi,
Lets say I have two tables, i.e:
TAB_A (colA1, colA2, colA3, colA4)
TAB_B (colB1, colB2, colB3, colB4) where colB2 is a FK to colA1
I am after an SQL query that will cater for both the following two scenarios.
Scenario 1:
TAB_A has two rows of data, i.e
(1, ABC100, 1, WG_A)
(2, ABC100, 2, WG_B)
TAB_B has one row of data, i.e
(1, 1, EMP_222, 4)
I use the following SQL:
select a.*, b.*
from tab_a a FULL OUTER JOIN tab_b b ON (a.colA1 = b.colB2)
where a.colA2 = 'ABC100'
This returns two rows:
1, ABC100, 1, WG_A, 1, 1, EMP_222, 4
2, ABC100, 2, WG_B
Now, what I actually would like my query to do is actually only return the row where a tab_b record exists, i.e, should only return one record:
1, ABC100, 1, WG_A, 1, 1, EMP_222, 4
This I can achieve by using a RIGHT OUTER JOIN instead above, but this causes issue with my scenario 2, which is the following set-up
Scenario 2:
TAB_A has only one row of data this time, i.e
(2, ABC100, 2, WG_B)
TAB_B has no data at all this time
This returns no rows but I actually now want this single record from tab_a returned.
I basically require an SQL query that will cater for both the top 2 scenarios, i.e, if a tab_b record exists from the outer join then only return this record along with tab_a data. If a tab_b record doesn't exist, then only return the tab_a record.
Hope the above makes sense.
Thanks.

Answer 1

Is it what you need (not very elegant) ?
SQL> select * from t_outer;
        ID CODE
         1 100
         2 100
SQL> select * from t_inner;
no rows selected
SQL> with tab1 as (
  2  select a.id a_id, a.code, b.id b_id from t_outer a join t_inner b on
  3  (a.id = b.id and a.code = '100'))
  4  select * from tab1
  5  union all
  6  select a.*, null from t_outer a where not exists (
  7  select 1 from tab1)
  8  and a.code = '100'
  9  /
      A_ID CODE             B_ID
         1 100
         2 100
SQL> insert into t_inner values(2);
1 row created.
SQL> with tab1 as (
  2  select a.id a_id, a.code, b.id b_id from t_outer a join t_inner b on
  3  (a.id = b.id and a.code = '100'))
  4  select * from tab1
  5  union all
  6  select a.*, null from t_outer a where not exists (
  7  select 1 from tab1)
  8  and a.code = '100'
  9  /
      A_ID CODE             B_ID
         2 100                 2
Rgds.