Decode in 'IN' clause doesn't work - any workaround?

Question

Hi All,
I thought this was working, but as I tested further I found it's not returning the right results. I have a query that is trying to take the first 4 letters of a string, and based on that value I want to limit the values in the 'IN ' clause. (Does that make sense?)
Something like this:
select * from table_a where NAME in
  select decode(substr(:P_var,1,4),'ABCD','(''ALF'',''BOB'',''COLE'')','EFGH','(''EVE'',''FRED'',''GORD'')') from dual
)But it seems that no matter what I do I can't get the right results.
This does return ('EVE','FRED','GORD') as the result of the nested select (P_var = 'EFGH'), but I get 'No Data Found', even though I know those names are in the table...
Not sure what would be a better way - AKA one that works, so any help is greatly appreciated...
Corey

Answer 1

Assuming you have collection type handy a couple of approaches spring to mind (note that MEMBER OF syntax in second example is 10g specific)...
Oracle Database 10g Release 10.2.0.2.0 - Production
SQL> CREATE TABLE table_a (name VARCHAR2 (30));
Table created.
SQL> CREATE OR REPLACE TYPE varchar2_table
  2     AS TABLE OF VARCHAR2 (4000);
  3  /
Type created.
SQL> INSERT INTO table_a
  2     SELECT *
  3     FROM   TABLE (varchar2_table (
  4               'ALF', 'BOB', 'COLE',
  5               'EVE', 'FRED', 'GORD',
  6               'TOM', 'DICK', 'HARRY'));
9 rows created.
SQL> COMMIT;
Commit complete.
SQL> VARIABLE p_var VARCHAR2 (30);
SQL> EXEC :p_var := 'ABCD';
PL/SQL procedure successfully completed.
SQL> SELECT a.*
  2  FROM   table_a a
  3  WHERe  a.name MEMBER OF (
  4            DECODE (SUBSTR (:p_var, 1, 4),
  5                'ABCD', VARCHAR2_TABLE ('ALF', 'BOB', 'COLE'),
  6                'EFGH', VARCHAR2_TABLE ('EVE', 'FRED', 'GORD')));
NAME
ALF
BOB
COLE
SQL> EXEC :p_var := 'EFGH';
PL/SQL procedure successfully completed.
SQL> SELECT a.*
  2  FROM   table_a a,
  3         TABLE (DECODE (SUBSTR (:p_var, 1, 4),
  4             'ABCD', VARCHAR2_TABLE ('ALF', 'BOB', 'COLE'),
  5             'EFGH', VARCHAR2_TABLE ('EVE', 'FRED', 'GORD'))) t
  6  WHERE  a.name = t.column_value;     
NAME
EVE
FRED
GORD
SQL>