JAVA必背面试题和项目面试通关要点 oracle必问的面试题.docVIP

JAVA必背面试题和项目面试通关要点 oracle必问的面试题 JAVA必背面试题和项目面试通关要点 JAVA必背面试题和项目面试通关要点 一 数据库 1.常问数据库查询、修改(SQL查询包含筛选查询、聚合查询和链接查询和优化问题，手写SQL语句，例如四个球队比赛，用SQL显示所有比赛组合;举例2：选择重复项，然后去掉重复项;) 数据库里的密码如何加密(md5); (1)数据库的密码加密:单向加密,insert into users (username,password) values (mike’,MD5(‘guessme’)); (2)双向加密:insert into users (username ,password) values (mike’,ENCODE(‘guessme’,’abanaafn’)); (3)SQL筛选查询:select * from user where user_id in (select user_id from user group by user_id having count(user_id)gt;1) order by user_id desc; (4)SQL聚合查询:select user_id from user group by user_id; (5)SQL衔接查询:内连接.select ,m.mess from student s inner join mark m on s.id=m.studentid;左外连接:select , m.mess from student s left join mark m on s.id=m.studentid;右外连接:select , m.mess from student s right join mark m on s.id=m.studentid;全外连接:select ,m.mess from student s full join mark m on s.id=m.studentid; (6)球队比赛组合:select count(*) from department as a ,department as b lt;gt;; (7)SQL选择重复语句:select id ,name from user where id in (select id from user group by id having count(1)gt;2);去除重复语句:select id from user group by id having count(*)gt;1; (8)数据库优化:prepareStatement比Statement性能高,一个sql发给服务器去执行.涉及步骤:语法检查,语义定义,编译和缓存.有外检约束会影响插入和删除功能,如果程序能保证数据的完整性,那么设计数据库的时候就去掉外键.sql语句全部大写,特别是列名和表名. 2. 如何实现数据库分页功能? SQL语句复杂的关联表查询，累计求和。 在不使用框架情况下，如何连接数据库? 数据库连接完之后，需要关闭的两个接口是什么? 关闭数据库过程中最容易抛出的异常是什么? (1)分页:”select * from user limit “+(pageNo-1)*pageSize+”,”+pageSize; (2)求和:select * from user1 union select * from user2; (3)手动连接数据库:Connection cn=null;PreparedStatement pst=null;Result rs=null;try{Class.forname(driverClassName);cn=DriverManager.getConnection(url,username,password);pst=cn.prepareStatement(“sql”);pst.setString(1,studentName);Result rs=pst.executeQuery();while(rs.next()){system.out.println();}catch(Exception e){e.printStackTrace();}finally{if(rs!=null){rs.close();}if(pst!=null){pst.close()}if(cn!=null){cn.close();}}} (4)Result prepareStatement 结果集和sql传输 (5)Exception 3. Oracle索引的优缺点、视图和存储过程、连接符是什么?默认端口是什么?MySQL什么是左链接、右链接