使用范围： 用于with clause。
作用： 针对with中的查询，先建立一个 global temporary table， 之后查询这个临时表。执行某些sql的时候，特别是多次使用with子查询的时候，会提升速度。
与之相对还有一个inline hint, Oracle指示所有的部分查询不使用TEMP TABLE TRANSFORMATION。
SQL> CREATE TABLE t0103_1 NOLOGGING AS SELECT * FROM dba_objects where ROWNUM<10000;
Table created.
SQL> with tmp as (select * from t0103) select * from tmp;
Execution Plan
----------------------------------------------------------
Plan hash value: 2929628763
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 999 | 87912 | 174 (0)| 00:00:03 |
| 1 | TABLE ACCESS FULL| T0103 | 999 | 87912 | 174 (0)| 00:00:03 |
---------------------------------------------------------------------------
SQL> with tmp as (select /*+ materialize */ * from t0103) select * from tmp;
Execution Plan
----------------------------------------------------------
Plan hash value: 877440232
--------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 999 | 201K| 178 (0)| 00:00:03 |
| 1 | TEMP TABLE TRANSFORMATION | | | | | |
| 2 | LOAD AS SELECT | SYS_TEMP_0FD9D660B_1690D1 | | | | |
| 3 | TABLE ACCESS FULL | T0103 | 999 | 87912 | 174 (0)| 00:00:03 |
| 4 | VIEW | | 999 | 201K| 4 (0)| 00:00:01 |
| 5 | TABLE ACCESS FULL | SYS_TEMP_0FD9D660B_1690D1 | 999 | 87912 | 4 (0)| 00:00:01 |
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参考： http://dioncho.wordpress.com/tag/inline/
http://caohong286.iteye.com/blog/1528711