Joins on different fields based on a condition

Question

Hi,
I have 2 tables, each consists of 5 fields, based on Field3's data, I want to join either F1 & F2 or F4 & F5.
I have given below the field creation and sample data for your reference. When I run the SQL with "case when .."
statement, it gives "ORA-00905: missing keyword" error.
I can do this by splitting into 2 separate SQL statements one for F1 & F2 and the other for F4 and F5.
Is there any other better way of doing it in a single SELECT statement?
Please share your views, thank you.
create table tmp_a
(f1 varchar2(50),
f2 varchar2(50),
f3 char(1),
f4 varchar2(50),
f5 varchar2(50))
create table tmp_b
(f1 varchar2(50),
f2 varchar2(50),
f3 char(1),
f4 varchar2(50),
f5 varchar2(50))
begin
     insert into tmp_a
     values('R1', 'abc', 'L', 'A1', 'B1');
     insert into tmp_a
     values('R2', 'lkj', 'L', 'A2', 'B2');
     insert into tmp_a
     values('R3', 'qwe', 'M', 'A3', 'B3');
     insert into tmp_a
     values('R4', '123', 'M', 'A4', 'B4');
     insert into tmp_b
     values('R3', 'qwe', 'L', 'A1', 'B1');
     insert into tmp_b
     values('R2', 'lkj', 'L', 'A2', 'B2');
     insert into tmp_b
     values('R4', '123', 'M', 'A3', 'B3');
     insert into tmp_b
     values('R1', 'abc', 'M', 'A3', 'B3');
     commit;
end;
select * from tmp_a;
select * from tmp_b;
select a.*, b.*
from tmp_a a, tmp_b b
where a.f1 = b.f1 and a.f2 = b.f2;
select a.*, b.*
from tmp_a a, tmp_b b
where a.f4 = b.f4 and a.f5 = b.f5;
select a.*, b.*
from tmp_a a, tmp_b b
where case when a.f3 = 'L' then
          a.f4 = b.f4 and a.f5 = b.f5
     else
          a.f1 = b.f1 and a.f2 = b.f2
end;

Answer 1

Maybe something like:
SQL> SELECT a.*, b.*
  2    FROM tmp_a a, tmp_b b
  3   WHERE CASE
  4            WHEN a.f3 = 'L'
  5               THEN a.f4
  6            ELSE a.f1
  7         END = CASE
  8                 WHEN a.f3 = 'L'
  9                    THEN b.f4
10                 ELSE b.f1
11              END
12     AND CASE
13            WHEN a.f3 = 'L'
14               THEN a.f5
15            ELSE a.f2
16         END = CASE
17                 WHEN a.f3 = 'L'
18                    THEN b.f5
19                 ELSE b.f2
20              END
21  /
F1         F2         F F4         F5         F1         F2         F F4         F5
R1         abc        L A1         B1         R3         qwe        L A1         B1
R2         lkj        L A2         B2         R2         lkj        L A2         B2
R3         qwe        M A3         B3         R3         qwe        L A1         B1
R4         123        M A4         B4         R4         123        M A3         B3
4 rows selected.Regards,
Jo
Edited by: Joice John on Jul 17, 2009 4:30 AM
Sigh!!! Sean you are too fast for me.... ;)