SQL优化经典案例----让in/exists子查询作为驱动表

SQL优化经典案例----让in/exists子查询作为驱动表

---http://blog.sina.com.cn/s/blog_61cd89f60102efam.html

在NL连接方式中，用小表或小的结果集作业驱动表，是提高SQL执行效率的重要因素之一，下面我们看一下让in/exists子查询作为驱动表优化的案例

select rowid rid

from its_car_pass7 v

where 1 = 1

and pass_datetime >=

to_date('2013-07-06 :17:46:04', 'yyyy-mm-dd hh24:mi:ss')

and pass_datetime <=

to_date('2013-07-06 :18:46:06', 'yyyy-mm-dd hh24:mi:ss')

and v.pass_device_unid in

(select unid

from its_base_device

where dev_bay_unid in ('01685EFE4658C19D59C4DDAAEDD37393')

and dev_type = '1'

and dev_chk_flag = '1'

and dev_delete_flag = 'N')

order by v.pass_datetime asc

Execution Plan





Predicate Information (identified by operation id):

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

5 - access("PASS_DATETIME">=TO_DATE(' 2013-07-06 17:46:04', 'syyyy-mm-dd hh24:mi:ss') AND

"PASS_DATETIME"<=TO_DATE(' 2013-07-06 18:46:06', 'syyyy-mm-dd hh24:mi:ss'))

filter("PASS_DATETIME">=TO_DATE(' 2013-07-06 17:46:04', 'syyyy-mm-dd hh24:mi:ss') AND

"PASS_DATETIME"<=TO_DATE(' 2013-07-06 18:46:06', 'syyyy-mm-dd hh24:mi:ss'))

6 - access("V"."PASS_DEVICE_UNID"="UNID")

7 - filter("DEV_BAY_UNID"='01685EFE4658C19D59C4DDAAEDD37393' AND "DEV_TYPE"='1' AND

"DEV_DELETE_FLAG"='N' AND "DEV_CHK_FLAG"='1')

Statistics

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

1 recursive calls

0 db block gets

110973 consistent gets

0 physical reads

0 redo size

47861 bytes sent via SQL*Net to client

1656 bytes received via SQL*Net from client

105 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

1560 rows processed

查看outline部分信息

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY(NULL, NULL, 'ADVANCED -PROJECTION'));

Outline Data

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





SQL优化后：

select

rowid
rid

from its_car_pass7 v

where 1 = 1

and pass_datetime >=

to_date('2013-07-06 :17:46:04', 'yyyy-mm-dd hh24:mi:ss')

and pass_datetime <=

to_date('2013-07-06 :18:46:06', 'yyyy-mm-dd hh24:mi:ss')

and v.pass_device_unid in

(select unid

from its_base_device

where dev_bay_unid in ('01685EFE4658C19D59C4DDAAEDD37393')

and dev_type = '1'

and dev_chk_flag = '1'

and dev_delete_flag = 'N')

order by v.pass_datetime asc

优化后执行计划信息





Statistics

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

1 recursive calls

0 db block gets

18645 consistent gets

130 physical reads

0 redo size

47861 bytes sent via SQL*Net to client

1657 bytes received via SQL*Net from client

105 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

1560 rows processed

优化效果还是不错的，逻辑读有原有的 110973 变为：18645