Oracle的SQL优化二

收到开发提交的一条SQL，在高并发下较慢，看能否做一些优化：

该SQL是1个表对另一个表做Left join,首先执行下看看，

SQL> select l.vcno,opttype,add_points,optdate,remark,memid,id,FAMILYID,create_Username,billno,billtype,billsubcase,reduce_Points, l.addnum,addpresentum,reducenum,reducepresentnum

2 from HQ_07310066.m_mempoint_logs l left join HQ_07310066.m_memdetail m on l.vcno = m.vcno where 1=1 AND l.memid = 'WX000000361' order by optdate desc;

已选择208行。

执行计划

----------------------------------------------------------

Plan hash value: 2095947206

--------------------------------------------------------------------------------------

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

--------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 4 | 464 | 172 (2)| 00:00:03 |

| 1 | SORT ORDER BY | | 4 | 464 | 172 (2)| 00:00:03 |

|* 2 | TABLE ACCESS FULL| M_MEMPOINT_LOGS | 4 | 464 | 171 (1)| 00:00:03 |

--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

2 - filter("L"."MEMID"='WX000000361')

统计信息

----------------------------------------------------------

0 recursive calls

0 db block gets

626 consistent gets

0 physical reads

0 redo size

7125 bytes sent via SQL*Net to client

663 bytes received via SQL*Net from client

15 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

208 rows processed

可能是主外键约束的原因，优化器自动对HQ_07310066.m_memdetail做了表消除。所以如果确定两表之间存在严格的主外键约束，可以直接在SQL中把不需要的表去掉，如下：

SQL> select l.vcno,opttype,add_points,optdate,remark,memid,id,FAMILYID,create_Username,billno,billtype,billsubcase,reduce_Points, l.addnum,addpresentum,reducenum,

2 reducepresentnum

3 from HQ_07310066.m_mempoint_logs l

4 where l.memid = 'WX000000361'

5 order by optdate desc;

已选择208行。

已用时间: 00: 00: 00.02

执行计划

----------------------------------------------------------

Plan hash value: 2095947206

--------------------------------------------------------------------------------------

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

--------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 4 | 464 | 172 (2)| 00:00:03 |

| 1 | SORT ORDER BY | | 4 | 464 | 172 (2)| 00:00:03 |

|* 2 | TABLE ACCESS FULL| M_MEMPOINT_LOGS | 4 | 464 | 171 (1)| 00:00:03 |

--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

2 - filter("L"."MEMID"='WX000000361')

统计信息

----------------------------------------------------------

1 recursive calls

0 db block gets

626 consistent gets

0 physical reads

0 redo size

11245 bytes sent via SQL*Net to client

663 bytes received via SQL*Net from client

15 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

208 rows processed

再创建索引：create index HQ_07310066.i_m_mempoint_logs_optdate on HQ_07310066.m_mempoint_logs(optdate);

SQL> select l.vcno,opttype,add_points,optdate,remark,memid,id,FAMILYID,create_Username,billno,billtype,billsubcase,reduce_Points, l.addnum,addpresentum,reducenum,

2 reducepresentnum

3 from HQ_07310066.m_mempoint_logs l

4 where l.memid = 'WX000000361'

5 order by optdate desc;

已选择208行。

已用时间: 00: 00: 00.02

执行计划

----------------------------------------------------------

Plan hash value: 3466595853

----------------------------------------------------------------------------------------------------------

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

----------------------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 4 | 464 | 6 (17)| 00:00:01 |

| 1 | SORT ORDER BY | | 4 | 464 | 6 (17)| 00:00:01 |

| 2 | TABLE ACCESS BY INDEX ROWID| M_MEMPOINT_LOGS | 4 | 464 | 5 (0)| 00:00:01 |

|* 3 | INDEX RANGE SCAN | I_M_MEMPOINT_LOGS_OPTDATE | 4 | | 1 (0)| 00:00:01 |

----------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

---------------------------------------------------

3 - access("L"."MEMID"='WX000000361')

统计信息

----------------------------------------------------------

1 recursive calls

0 db block gets

44 consistent gets

2 physical reads

0 redo size

11245 bytes sent via SQL*Net to client

663 bytes received via SQL*Net from client

15 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

208 rows processed

优化完成。