Dinamic query

Question

Hello!
For first, sorry for my ignorance, but I'm not DBA and who is DBA at my company couldn't help me (I don't know why!).
I have a problem with dinamic filters in some queries.
I want to select N rows of a table, but the query can vary in a series of filters, it depending on the parameters.
For example:
first case:
SELECT X FROM TABLE
WHERE X = 'TEST';
second case:
SELECT X FROM TABLE
WHERE X = 'TEST'
OR X = 'AAA';
Did you understand? This is the problem. How can I concatenate this clause "OR" in the end of the query when I want, without create it as a string and using "EXECUTE SQL"...?
I want to use it as a dinamic command...
One more time, sorry if this is a question that only fools do. I'm learning by myself, and at the moment I'm lost. =)
Thanks!

Answer 1

in this case performance problem occurs for the NULL case only?
create table tab (x varchar2(16));
insert into tab values ('TEST');
insert into tab values ( NULL );
begin
   for i in 1..1000000 loop
       insert into tab values ( to_char(i) );
   end loop;
end;
create unique index ui_tab_x on tab(x) nologging;
exec dbms_stats.gather_table_stats(user, 'tab');
commit;
set timing on
set autotrace traceonly
SELECT X FROM tab WHERE X = 'TEST' or X = DECODE(1,NULL,X,1) ;
Elapsed: 00:00:00.00
Execution Plan
Plan hash value: 3421616299
| Id  | Operation          | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |          |     2 |    12 |     4   (0)| 00:00:01 |
|   1 |  CONCATENATION     |          |       |       |            |          |
|* 2 | INDEX UNIQUE SCAN| UI_TAB_X | 1 | 6 | 2 (0)| 00:00:01 |
|* 3 | INDEX UNIQUE SCAN| UI_TAB_X | 1 | 6 | 2 (0)| 00:00:01 |
Predicate Information (identified by operation id):
2 - access("X"='TEST')
3 - access("X"='1')
Statistics
          1  recursive calls
          0  db block gets
6 consistent gets
          0  physical reads
          0  redo size
        444  bytes sent via SQL*Net to client
        384  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          2  rows processed
SELECT X FROM tab WHERE X = 'TEST' or X = DECODE(NULL,NULL,X,NULL) ;
1000001 rows selected.
Elapsed: 00:00:05.87
Execution Plan
Plan hash value: 1995730731
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |      |     1 |     6 |   503   (9)| 00:00:07 |
|* 1 | TABLE ACCESS FULL| TAB | 1 | 6 | 503 (9)| 00:00:07 |
Predicate Information (identified by operation id):
1 - filter("X"="X" OR "X"='TEST')
Statistics
          1  recursive calls
          0  db block gets
68353 consistent gets
          0  physical reads
          0  redo size
   16555973  bytes sent via SQL*Net to client
     733710  bytes received via SQL*Net from client
      66668  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
    1000001  rows processedwhat is your Oracle version? I did above test on 10gR2. And are you using bind variables for this operation?
if you are using bind variables force the NOT NULL cases to be parsed differently than NULL case, so guarantee for different execution plans no matter which comes first.
one way to do this can be with an if block and use comments in your code.
if arg is NOT NULL then
   select /* NOT null case */ X FROM tab WHERE X = 'TEST' or X = DECODE(arg,NULL,X,arg) ;
else
   select /* null case */ X FROM tab WHERE X = 'TEST' or X = DECODE(arg,NULL,X,arg) ;
end if;