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이 문서는 읽기 전용입니다. 원본을 볼 수는 있지만 바꿀 수는 없습니다. 문제가 있다고 생각하면 관리자에게 문의하세요.
==== 그냥 참조용. ====



SQL> select department_id from employees;

DEPARTMENT_ID
-------------
           90
           90
           90
           60
           60
           60
           50
           50
           50
           50
           50
           80
           80
           80

           10
           20
           20
          110
          110

20 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 1445457117

-------------------------------------------------------------------------------
| Id  | Operation         | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |           |    20 |    60 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| EMPLOYEES |    20 |    60 |     3   (0)| 00:00:01 |
-------------------------------------------------------------------------------

SQL> ed
Wrote file afiedt.buf

  1  select department_id from employees
  2* group by department_id
SQL> /

DEPARTMENT_ID
-------------

           90
           20
          110
           50
           80
           60
           10

8 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 1192169904

--------------------------------------------------------------------------------
| Id  | Operation          | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |           |     7 |    21 |     4  (25)| 00:00:01 |
|   1 |  HASH GROUP BY     |           |     7 |    21 |     4  (25)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMPLOYEES |    20 |    60 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------------

SQL> select distinct department_id from employees;

DEPARTMENT_ID
-------------

           90
           20
          110
           50
           80
           60
           10

8 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 3042654289

--------------------------------------------------------------------------------
| Id  | Operation          | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |           |     7 |    21 |     4  (25)| 00:00:01 |
|   1 |  HASH UNIQUE       |           |     7 |    21 |     4  (25)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMPLOYEES |    20 |    60 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------------
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