Return Set Amount Of Rows

Question

Hello All,
Quick question I hope... How do I request a set amount of terms and have the Oracle Agent stop, once the amount of rows has been reached.
I am not looking for (example):
select * from
(SELECT rownum ROW_NUM, empID, empName FROM employees)
where empName like '%SM%'
AND
ROW_NUM <= 10
This works in most cases, but Oracle is still evaluating all results, and only returning rows where the ROW_NUM meets the criteria. If I have a million rows with matching empName , and only want to return 10 results it still evaluates all million rows. and break the query, this does not work...

Answer 1

Statement 1 is faster - rownum criteria is used along with the last_name
Statement 2 is slower - rownum criteria is used after all the last names are fetched.
--#1
SQL> select first_name, last_name from emp2 where last_name like 'W%' and rownum < 10 ;
FIRST_NAME           LAST_NAME
Alana                Walsh
Alana                Walsh
Alana                Walsh
Alana                Walsh
Alana                Walsh
Alana                Walsh
Alana                Walsh
Alana                Walsh
Alana                Walsh
9 rows selected.
Execution Plan
Plan hash value: 3151743630
| Id  | Operation                    | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT             |       |    "9"|   234 |    13   (0)| 00:00:01 |
|*  1 |  COUNT STOPKEY               |       |       |       |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| EMP2  |  5145 |   130K|    13   (0)| 00:00:01 |
|*  3 |    INDEX RANGE SCAN          | EMP2X |       |       |     3   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter(ROWNUM<10)
   3 - access("LAST_NAME" LIKE 'W%')
       filter("LAST_NAME" LIKE 'W%')
Note
   - dynamic sampling used for this statement
Statistics
         15  recursive calls
          0  db block gets
        157  consistent gets
          8  physical reads
          0  redo size
        552  bytes sent via SQL*Net to client
        380  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          9  rows processed
--#2
SQL> select * from ( select first_name, last_name, rownum rn from emp2 where last_name like 'W%'  ) where  rn< 10 ;
FIRST_NAME           LAST_NAME                         RN
Matthew              Weiss                              1
Alana                Walsh                              2
Jennifer             Whalen                             3
Matthew              Weiss                              4
Alana                Walsh                              5
Jennifer             Whalen                             6
Matthew              Weiss                              7
Alana                Walsh                              8
Jennifer             Whalen                             9
9 rows selected.
Execution Plan
Plan hash value: 2594185790
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT    |      | "5145"|   195K|   619   (3)| 00:00:08 |
|*  1 |  VIEW               |      |  5145 |   195K|   619   (3)| 00:00:08 |
|   2 |   COUNT             |      |       |       |            |          |
|*  3 |    TABLE ACCESS FULL| EMP2 |  5145 |   130K|   619   (3)| 00:00:08 |
Predicate Information (identified by operation id):
   1 - filter("RN"<10)
   3 - filter("LAST_NAME" LIKE 'W%')
Note
   - dynamic sampling used for this statement
Statistics
         13  recursive calls
          0  db block gets
       2371  consistent gets
          0  physical reads
          0  redo size
        745  bytes sent via SQL*Net to client
        380  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          9  rows processed