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--方法一: select a.id,a.SName,a.ClsNo,a.Score from Table1 a left join Table1 b on a.ClsNo=b.ClsNo and a.Score(select count(*) from Table1 where ClsNo=a.ClsNo and Score>a.Score) order by a.ClsNo... 阅读全文
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隔离级别(isolation level):定义了事务与事务之间的隔离程度,隔离级别与并发性是互为矛盾的: 隔离程度越高,数据库的并发性越差;隔离程度越低,数据库的并发性越好。 ANSI/ISO SQL92标准定义了一些数据库操作的隔离级别: 1.未提交读(read uncommitted)脏读 2.提交读(read committed)非重复读 3.重复读(repeatable rea... 阅读全文
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delete from test1 where (id,name )in (select * from ( select id,name from test1 group by id,name having (count(*)>1) ) a) and num not in(select * from ( select min(num) from t... 阅读全文
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row_number() over(partition by ... order by ...) rank() over(partition by ... order by ...) dense_rank() over(partition by ... order by ...) count() over(partition by ... order by ...) max() over... 阅读全文
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Lifecycle:(接口) LifecycleBase:abstract:添加,删除Listener,各种init,start,stop,destory LifecycleMBeanBase:abstract,注册各种Mbean Connector:创建Request,Response ContainerBase ... 阅读全文
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------------------------------------------------------------------------------------------------------------------------ RMI 客户端-->远程对象的存根(stub)-->网格-->远程对象的骨架(skeleton)-->远程对象(服务器) Remote:接口,用于标识其方法... 阅读全文
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Iterable接口, Iterator iterator() Collection:接口,add(E e) ,size() , Object[] toArray() List:接口,get(int index) ,Iterator iterator() ,ListIterator listIterator() ArrayList:类, ... 阅读全文
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package mbeanTest; import java.util.Set; import javax.management.Attribute; import javax.management.MBeanOperationInfo; import javax.management.MBeanServer; import javax.management.MBeanServerFacto... 阅读全文
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package mbeanTest; import java.lang.reflect.Constructor; import javax.management.Descriptor; import javax.management.InstanceNotFoundException; import javax.management.MBeanException; import javax.... 阅读全文
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package mbeanTest; public interface HelloWorldMBean { public String getHello(); public void setHello(String hello); public Object getInstance(); public String message(String ms); ... 阅读全文