sql 执行计划 view是什么意思啊

Question

------------------------------------------------------------------------------------------
| Id  | Operation             | Name             | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |                  |     1 |   370 |     8  (25)| 00:00:01 |
|*  1 |  HASH JOIN            |                  |     1 |   370 |     8  (25)| 00:00:01 |
|   2 |   TABLE ACCESS FULL   | TBL_SERV         |     1 |    34 |     2   (0)| 00:00:01 |
|   3 |   VIEW                |                  |     1 |   336 |     6  (34)| 00:00:01 |
|   4 |    HASH GROUP BY      |                  |     1 |   454 |     6  (34)| 00:00:01 |
|*  5 |     HASH JOIN         |                  |     1 |   454 |     5  (20)| 00:00:01 |
|*  6 |      TABLE ACCESS FULL| TBL_EPG          |     1 |   181 |     2   (0)| 00:00:01 |
|   7 |      TABLE ACCESS FULL| TBL_IPTV_CHANNEL |     1 |   273 |     2   (0)| 00:00:01 |
------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - access("A"."USER_ID"="C"."ACC_NBR")
   5 - access("A"."CODE"="B"."CODE")
   6 - filter(("A"."SERVICE_MODE"=1 OR "A"."SERVICE_MODE"=2) AND
              "A"."E_TIME">='20110607000000' AND "A"."E_TIME"<='20110607235959')

Answer 1

把下面hash group by结果看作一个视图方式来使用

Answer 2

oracle 嵌套视图：
select * from (
select col_name from table_name
where exists(
)
)