select para_id
  from dwf.f_Savc_Buscode b
 where b.Para_Id = (SELECT MIN(Para_Id)
                      FROM Dwf.f_Savc_Buscode
                     WHERE Bus_Code = b.Bus_Code);

SQL> set linesize 200
SQL> set pagesize 200
SQL> explain plan for select para_id
  from dwf.f_Savc_Buscode b
 where b.Para_Id = (SELECT MIN(Para_Id)
                      FROM Dwf.f_Savc_Buscode
                     WHERE Bus_Code = b.Bus_Code);  2    3    4    5  

Explained.

SQL> select * from table(dbms_xplan.display());

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1952012934

----------------------------------------------------------------------------------------
| Id  | Operation		| Name	       | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	|	       |    86 |  2924 |     7	(15)| 00:00:01 |
|*  1 |  HASH JOIN		|	       |    86 |  2924 |     7	(15)| 00:00:01 |
|   2 |   VIEW			| VW_SQ_1      |    86 |  2236 |     4	(25)| 00:00:01 |
|   3 |    HASH GROUP BY	|	       |    86 |   688 |     4	(25)| 00:00:01 |
|   4 |     INDEX FAST FULL SCAN| SYS_C0036092 |   435 |  3480 |     3	 (0)| 00:00:01 |
|   5 |   INDEX FAST FULL SCAN	| SYS_C0036092 |   435 |  3480 |     3	 (0)| 00:00:01 |
----------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("B"."PARA_ID"="MIN(PARA_ID)" AND "ITEM_1"="B"."BUS_CODE")

17 rows selected.

改寫為with as 後:
with A as (select para_id,min(Para_Id) over(partition by Bus_Code) min_para_id 
from Dwf.f_Savc_Buscode)
select para_id from A where A.para_id=a.min_para_id
SQL> explain plan for with A as (select para_id,min(Para_Id) over(partition by Bus_Code) min_para_id 
from Dwf.f_Savc_Buscode)
select para_id from A where A.para_id=a.min_para_id  2    3  ;

Explained.

SQL> select * from table(dbms_xplan.display());

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1562643515

---------------------------------------------------------------------------------------
| Id  | Operation	       | Name	      | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT       |	      |   435 | 11310 |     4  (25)| 00:00:01 |
|*  1 |  VIEW		       |	      |   435 | 11310 |     4  (25)| 00:00:01 |
|   2 |   WINDOW SORT	       |	      |   435 |  3480 |     4  (25)| 00:00:01 |
|   3 |    INDEX FAST FULL SCAN| SYS_C0036092 |   435 |  3480 |     3	(0)| 00:00:01 |
---------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("A"."PARA_ID"="A"."MIN_PARA_ID")

15 rows selected.


SQL> select * from (with A as (select para_id,min(Para_Id) over(partition by Bus_Code) min_para_id 
from Dwf.f_Savc_Buscode)
select para_id from A where A.para_id=a.min_para_id)
minus
select para_id
  from dwf.f_Savc_Buscode b
 where b.Para_Id = (SELECT MIN(Para_Id)
                      FROM Dwf.f_Savc_Buscode
                     WHERE Bus_Code = b.Bus_Code)  2    3    4    5    6    7    8    9  ;

no rows selected