Question

hash join 和 nested loop 连接的区别 oracle开发过程中如何去查看连接方式

Answer 1

通过autotrace来查看
例如
SQL> set autotrace on
SQL> select a.* from t1 a,t1 b where a.id=b.id;

no rows selected

Execution Plan
----------------------------------------------------------
Plan hash value: 1734879205

---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 39 | 5 (20)| 00:00:01 |
|* 1 | HASH JOIN | | 1 | 39 | 5 (20)| 00:00:01 |
| 2 | TABLE ACCESS FULL| T1 | 1 | 26 | 2 (0)| 00:00:01 |
| 3 | TABLE ACCESS FULL| T1 | 1 | 13 | 2 (0)| 00:00:01 |
---------------------------------------------------------------------------