DISTINCT 列添加索引

添加索引后，没啥效要，这方面优化没啥效果，如果项目要用到DISTINCT进行去重，需要再去确认基表关联，确认业务。

SQL> select t.object_id from t_distinct_tb t ;

已选择50631行。

已用时间:  00: 00: 00.71

执行计划
----------------------------------------------------------
Plan hash value: 1512865825

-----------------------------------------------------------------------------------
| Id  | Operation         | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |               | 50086 |   635K|   161   (2)| 00:00:02 |
|   1 |  TABLE ACCESS FULL| T_DISTINCT_TB | 50086 |   635K|   161   (2)| 00:00:02 |
-----------------------------------------------------------------------------------

Note
-----
- dynamic sampling used for this statement

统计信息
----------------------------------------------------------
50  recursive calls
0  db block gets
4109  consistent gets
696  physical reads
0  redo size
732835  bytes sent via SQL*Net to client
37510  bytes received via SQL*Net from client
3377  SQL*Net roundtrips to/from client
0  sorts (memory)
0  sorts (disk)
50631  rows processed

SQL> select distinct t.object_id from t_distinct_tb t ;

已选择50631行。

已用时间:  00: 00: 00.56

执行计划
----------------------------------------------------------
Plan hash value: 3170339755

--------------------------------------------------------------------------------------------
| Id  | Operation          | Name          | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |               | 50086 |   635K|       |   406   (3)| 00:00:05 |
|   1 |  HASH UNIQUE       |               | 50086 |   635K|  1976K|   406   (3)| 00:00:05 |
|   2 |   TABLE ACCESS FULL| T_DISTINCT_TB | 50086 |   635K|       |   161   (2)| 00:00:02 |
--------------------------------------------------------------------------------------------

Note
-----
- dynamic sampling used for this statement

统计信息
----------------------------------------------------------
4  recursive calls
0  db block gets
767  consistent gets
0  physical reads
0  redo size
732835  bytes sent via SQL*Net to client
37510  bytes received via SQL*Net from client
3377  SQL*Net roundtrips to/from client
0  sorts (memory)
0  sorts (disk)
50631  rows processed

SQL>
SQL> select distinct t.object_id from t_distinct_tb t ;

已选择50631行。

已用时间:  00: 00: 00.51

执行计划
----------------------------------------------------------
Plan hash value: 3170339755

--------------------------------------------------------------------------------------------
| Id  | Operation          | Name          | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |               | 50086 |   635K|       |   406   (3)| 00:00:05 |
|   1 |  HASH UNIQUE       |               | 50086 |   635K|  1976K|   406   (3)| 00:00:05 |
|   2 |   TABLE ACCESS FULL| T_DISTINCT_TB | 50086 |   635K|       |   161   (2)| 00:00:02 |
--------------------------------------------------------------------------------------------

Note
-----
- dynamic sampling used for this statement

统计信息
----------------------------------------------------------
5  recursive calls
0  db block gets
768  consistent gets
0  physical reads
0  redo size
732835  bytes sent via SQL*Net to client
37510  bytes received via SQL*Net from client
3377  SQL*Net roundtrips to/from client
0  sorts (memory)
0  sorts (disk)
50631  rows processed