FULL Hint可以提升优化器对指定表走全表扫描，但是FULL提示一次只能对一个表起作用
SQL> select ename,dept.deptno from emp,dept where emp.deptno=dept.deptno;
已选择14行。
执行计划
----------------------------------------------------------
Plan hash value: 3074306753
------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 14 | 168 | 3 (0)| 00:00:01 |
| 1 | NESTED LOOPS | | 14 | 168 | 3 (0)| 00:00:01 |
| 2 | TABLE ACCESS FULL| EMP | 14 | 126 | 3 (0)| 00:00:01 |
|* 3 | INDEX UNIQUE SCAN| PK_DEPT | 1 | 3 | 0 (0)| 00:00:01 |
------------------------------------------------------------------------------
SQL> select /*+ full(dept) */ ename,dept.deptno from emp,dept where emp.deptno=dept.deptno;
已选择14行。
执行计划
----------------------------------------------------------
Plan hash value: 615168685
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 14 | 168 | 7 (15)| 00:00:01 |
|* 1 | HASH JOIN | | 14 | 168 | 7 (15)| 00:00:01 |
| 2 | TABLE ACCESS FULL| DEPT | 4 | 12 | 3 (0)| 00:00:01 |
| 3 | TABLE ACCESS FULL| EMP | 14 | 126 | 3 (0)| 00:00:01 |
SQL> select /*+ full(dept,emp) */ ename,dept.deptno from emp,dept where emp.deptno=dept.deptno;
已选择14行。
执行计划
----------------------------------------------------------
Plan hash value: 3074306753
------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 14 | 168 | 3 (0)| 00:00:01 |
| 1 | NESTED LOOPS | | 14 | 168 | 3 (0)| 00:00:01 |
| 2 | TABLE ACCESS FULL| EMP | 14 | 126 | 3 (0)| 00:00:01 |
|* 3 | INDEX UNIQUE SCAN| PK_DEPT | 1 | 3 | 0 (0)| 00:00:01 |
------------------------------------------------------------------------------
可见FULL提升失效，full只能对一个表指定全表扫描，如果想要对多个表执行全表扫描，使用多个full提升。