Sql decode help

Question

I have the following 3 tables:
Table A
Id (Number)
Id#2 (Number)
Type (Number)
Table B
Id#2 (Number)
Decription (Varchar2)
Table C
Id#2 (Number)
Decription (Varchar2)
I want to write a select statement that would return:
Id from Table A,
Description (If type in Table A = 1 then get description from Table B, if type in Table A= 2 then get description from Table C)
Can anyone please help?

Answer 1

Well, one of the things I've learned is "It always depends, you always need to test the defferent scenario's.."
But still I have to agree on this one with you, see the results I got:
SQL> select banner from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE    10.2.0.4.0      Production
TNS for IBM/AIX RISC System/6000: Version 10.2.0.4.0 - Productio
NLSRTL Version 10.2.0.4.0 - Production
Elapsed: 00:00:00.03
SQL> set autotrace traceonly
SQL> drop table a;
Table dropped.
Elapsed: 00:00:00.37
SQL> drop table b;
Table dropped.
Elapsed: 00:00:00.34
SQL> drop table c;
Table dropped.
Elapsed: 00:00:00.32
SQL> create table a  as
  2  select level id,
  3         level id2,
  4         case when rownum <= 500000 then 1 else 2 end type
  5  from dual
  6  connect by level <= 100000;
Table created.
Elapsed: 00:00:08.18
SQL> create table b  as
  2  select level id2, 'description table b' description
  3  from dual
  4  connect by level <= 50000;
Table created.
Elapsed: 00:00:01.06
SQL> create table c  as
  2  select 50000+level id2, 'description table c' description
  3  from dual
  4  connect by level <= 50000;
Table created.
Elapsed: 00:00:01.67
SQL> alter table a modify id primary key;
Table altered.
Elapsed: 00:00:01.06
SQL> alter table b modify id2 primary key;
Table altered.
Elapsed: 00:00:00.37
SQL> alter table c modify id2 primary key;
Table altered.
Elapsed: 00:00:00.37
SQL> begin
  2   dbms_stats.gather_table_stats(user, 'A');
  3   dbms_stats.gather_table_stats(user, 'B');
  4   dbms_stats.gather_table_stats(user, 'C');
  5  end;
  6  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.68
SQL> SELECT a.id,
  2         CASE
  3           WHEN a.TYPE = 1 THEN
  4            b.description
  5           WHEN a.TYPE = 2 THEN
  6            c.description
  7         END description
  8    FROM a,
  9         b,
10         c
11   WHERE a.id2 = b.id2(+)
12     AND a.id2 = c.id2(+);
100000 rows selected.
Elapsed: 00:00:11.06
Execution Plan
Plan hash value: 1054766904
| Id  | Operation              | Name | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT       |      |   100K|  5859K|       |   676   (1)| 00:00:09 |
|*  1 |  HASH JOIN RIGHT OUTER |      |   100K|  5859K|  1728K|   676   (1)| 00:00:09 |
|   2 |   TABLE ACCESS FULL    | C    | 49082 |  1150K|       |    50   (0)| 00:00:01 |
|*  3 |   HASH JOIN RIGHT OUTER|      |   100K|  3515K|  1800K|   313   (1)| 00:00:04 |
|   4 |    TABLE ACCESS FULL   | B    | 51064 |  1196K|       |    50   (0)| 00:00:01 |
|   5 |    TABLE ACCESS FULL   | A    |   100K|  1171K|       |    60   (2)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - access("A"."ID2"="C"."ID2"(+))
   3 - access("A"."ID2"="B"."ID2"(+))
Statistics
          0  recursive calls
          0  db block gets
          0  consistent gets
          0  physical reads
          0  redo size
          0  bytes sent via SQL*Net to client
          0  bytes received via SQL*Net from client
          0  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
     100000  rows processed
SQL> select a.id,
  2         case
  3           when a.type = 1 then
  4            (select description from b b where b.id2 = a.id2)
  5           when a.type = 2 then
  6            (select description from c c where c.id2 = a.id2)
  7         end description
  8  from a a;
100000 rows selected.
Elapsed: 00:00:11.73
Execution Plan
Plan hash value: 3680219842
| Id  | Operation                    | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT             |              |   100K|  1171K|    60   (2)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID | B            |     1 |    24 |     1   (0)| 00:00:01 |
|*  2 |   INDEX UNIQUE SCAN          | SYS_C0022091 |     1 |       |     1   (0)| 00:00:01 |
|   3 |   TABLE ACCESS BY INDEX ROWID| C            |     1 |    24 |     1   (0)| 00:00:01 |
|*  4 |    INDEX UNIQUE SCAN         | SYS_C0022092 |     1 |       |     1   (0)| 00:00:01 |
|   5 |  TABLE ACCESS FULL           | A            |   100K|  1171K|    60   (2)| 00:00:01 |
Predicate Information (identified by operation id):
   2 - access("B"."ID2"=:B1)
   4 - access("C"."ID2"=:B1)
Statistics
          0  recursive calls
          0  db block gets
          0  consistent gets
          0  physical reads
          0  redo size
          0  bytes sent via SQL*Net to client
          0  bytes received via SQL*Net from client
          0  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
     100000  rows processedMy testcase differs from yours, since I added Primary Keys to the tables.
I thought that to be more realistic, I hope you'll agree on that.
That way the plan and time for the second query changes, ofcourse ;-) .
It would be nice to know from Dausboy if our testcases were more or less representative for his situation anyway.