用sys用户登录，给oe用户授权dba，以便可以用oe用户查看执行计划：
oe@OCM> conn / as sysdba
Connected.
sys@OCM> grant dba to oe;
Grant succeeded.
sys@OCM> conn oe/oe
Connected.
oe@OCM> set autot traceonly;
oe@OCM> SELECT p.product_name,i.item_cnt
2 FROM (SELECT product_id,COUNT(*) item_cnt
3 FROM order_items
4 GROUP BY product_id) i RIGHT OUTER JOIN products p ON i.product_id=p.product_id; 288 rows selected. Execution Plan
----------------------------------------------------------
Plan hash value: 1905807913 -----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 288 | 24768 | 97 (3)| 00:00:02 |
|* 1 | HASH JOIN RIGHT OUTER | | 288 | 24768 | 97 (3)| 00:00:02 |
| 2 | VIEW | index$_join$_006 | 288 | 11520 | 88 (2)| 00:00:02 |
|* 3 | HASH JOIN | | | | | |
|* 4 | INDEX FAST FULL SCAN| PRD_DESC_PK | 288 | 11520 | 41 (0)| 00:00:01 |
| 5 | INDEX FAST FULL SCAN| PROD_NAME_IX | 288 | 11520 | 68 (0)| 00:00:01 |
|* 6 | HASH JOIN RIGHT OUTER | | 288 | 13248 | 9 (12)| 00:00:01 |
| 7 | VIEW | | 185 | 4810 | 3 (0)| 00:00:01 |
| 8 | HASH GROUP BY | | 185 | 740 | 3 (0)| 00:00:01 |
| 9 | INDEX FULL SCAN | ITEM_PRODUCT_IX | 665 | 2660 | 3 (0)| 00:00:01 |
| 10 | TABLE ACCESS FULL | PRODUCT_INFORMATION | 288 | 5760 | 5 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------- Predicate Information (identified by operation id):
--------------------------------------------------- 1 - access("D"."PRODUCT_ID"(+)="I"."PRODUCT_ID")
3 - access(ROWID=ROWID)
4 - filter("D"."LANGUAGE_ID"=SYS_CONTEXT('USERENV','LANG'))
6 - access("I"."PRODUCT_ID"(+)="I"."PRODUCT_ID") Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
135 consistent gets
0 physical reads
0 redo size
14913 bytes sent via SQL*Net to client
733 bytes received via SQL*Net from client
21 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
288 rows processed
可以看看执行计划，了解一下sql 执行的步骤。
答案A是正确的：查询出结果288 行，说明可以正常执行并返回结果
答案B是不正确的：我们可以把内联视图看成是一个独立的表，它是可以与其它表做外连接的。
答案C是不正确的：内联视图聚合函数的别名可以看作一个列名展显出来
答案D是不正确的：group by可以用在内联视图
正确答案是：A
这道题目太简单了，没什么好说的，写过SQL的人，直接可以PASS了。