splay());
执行结果为：
[html]
1 Plan hash value: 1237158055
2
3 -----------------------------------------------------------------------------
4 | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
5 -----------------------------------------------------------------------------
6 | 0 | SELECT STATEMENT | | 24 | 576 | 32 (4)| 00:00:01 |
7 | 1 | HASH GROUP BY | | 24 | 576 | 32 (4)| 00:00:01 |
8 | 2 | VIEW | | 24 | 576 | 31 (0)| 00:00:01 |
9 | 3 | UNION-ALL | | | | | |
10 | 4 | TABLE ACCESS FULL| A | 10 | 30 | 14 (0)| 00:00:01 |
11 | 5 | TABLE ACCESS FULL| B | 5 | 15 | 14 (0)| 00:00:01 |
12 | 6 | TABLE ACCESS FULL| C | 9 | 189 | 3 (0)| 00:00:01 |
13 -----------------------------------------------------------------------------
14
15 Note
16 -----
17 - dynamic sampling used for this statement
对比2种处理方式，union all 的方式明显优于 full join。也可以看出简单的sql语句效率不一定好。