oracle_效率优化

1、并行和强制走索引的用法

SELECT/*+parallel(T 16) parallel(B 16) parallel(D 16)*/
 T.POLICY_NO,
 T.DEPARTMENT_CODE,
 T.PLAN_CODE,
   FROM EPCIS_AUTO_POLICY_BASE_INFO T ,
       EPCIS_AUTO_POLICY_VEHICLE_INFO B,
       EPCIS_AUTO_A_PRE_MID_RESULT D
 WHERE T.POLICY_NO = B.POLICY_NO
   AND T.APPLY_POLICY_NO = D.APPLY_POLICY_NO(+)
   AND T.LAST_BEGIN_DATE >=
       ADD_MONTHS(TRUNC(TO_DATE('20151101', 'YYYYMMDD'), 'YYYY'), 9)
   AND T.LAST_BEGIN_DATE <
       LEAST(TO_DATE('20151201', 'YYYYMMDD'),
             ADD_MONTHS(TRUNC(TO_DATE('20151101', 'YYYYMMDD'), 'YYYY'), 12))
   AND T.UNDERWRITE_TIME < TO_DATE('20151201', 'YYYYMMDD')

--强制走索引

seg是表的别名

/*+INDEX(SEG IDX_T_RES_ALLOSEG_ALLOID)*/

2、在用分析函数的时候一定要注意，再外面嵌套子查询的时候，会导致执行计划改变

虽然里层的sql单独查询很快，但是一旦套嵌上了子查询后，执行计划就会变化，并不是说只是的单纯的将里面的结果集外面再查询，否则也不会一直查不出来、、、

这种情况的原因是里层的where条件中某些条件需要查较大的表；可考虑优化里层的where条件；

结论：

　　只要以后用到分析函数的，where子句的的 in 或者not in 都换成 exists；　　

select * from (
select
t.in_calling_nbr as calling_nbr,
t.in_called_nbr as called_nbr,
t1.cp_name as cp_name,
t2.cn_simple_name as cn_simple_name,
t2.insert_code as insert_code,
decode(t.in_type,1,'豆豆大作战',2,'抢红包',3,'和教育豆豆',4,'随机抢红包') as jiemu_type,
'欧飞系统维护或者其他情况导致充值失败~~' as err_msg,
to_number(t.in_fee) as ordercash,
row_number()over (partition by t.in_type,t.in_calling_nbr,t.in_called_nbr,t.in_logdate order by t2.insert_code desc) as r_num
from autorecharge.recharge_log@ivrpro t,med_new.T_CP_CHANNLE_INFO@ivrpro t1,ani.ani_sp_service@ivrpro t2
where t.in_logdate >=date'2017-03-28'
and t.in_logdate <date'2017-03-29'
and t.flag = 1
and not exists (select 1 from (select * from autorecharge.oufei_charge_orderinfo_log@ivrpro
union all
select * from autorecharge.oufei_charge_orderinfo@ivrpro) m
where m.sporder_id = t.sporder_id
and m.create_date >= date'2017-03-28')

and substr(t.in_called_nbr,1,length(t2.insert_code)) = t2.insert_code
and t.in_called_nbr = t1.channle_id
)
where r_num =1 ;

　

优化后：

 Oracle中用一个表的数据更新另一个表的数据

①、普通的数据量较小时：

update tab1 set val=(select val from tab2 where tab1.id=tab2.id) [where exists (select 1 from tab2 where tab1.id=tab2.id)];

②、数据量比较多的话：

　　merge终极版：

　　merge into tab1  using  (select * from tab2 x  where x.rowid =  (select max(y.rowid) from tab2 y  where x.id = y.id)) tab2  on(tab1.id=tab2.id)  when

　　matched then  update set tab1.val = tab2.val