SQL3.0中的行类型
Array，数组Sturct，结构Blob，大的二进制数据文件。Clob，大文本文件对象。在使用上述大对象的时候，在使用JDBC插入记录时要先插入一个空的占位对象，然后使用select blobdata from t_blob where id = " + id + " for update 这样的语法来对获得的大对象，进行实际的写入操作 Blod通过getBinaryOutputStream()方法获取流进行写入。getBinaryStream()方法获得流来获取blob中存储的数据。 clob的操作也和blob相同。getAsciiStream() 方法用于读取存储的文本对象，getAsciiOutputStream()方法之获得流用来向文件对象写入的。第四季一、ID的High/Low算法 高位数字分别与低位数字相匹配，得到的数字是唯一的 减少与数据库的交互
二、ORM１、类映射成表 类名与表名对应２、属性定义映射成列，类型之间必须是兼容的３、类关系映射成表关系
一对一双向关系内存中都保存对方的一个引用数据库中，表b的id是主键，也是外键，引用a表的id主键 －－ share pk 表b中有一个字段aid是外键，引用a表的主键，并且有唯一约束 －－ pk+fk共享主键：create table car_pk ( id number(10,0) not null, name varchar2(15), serial varchar2(30), manufacturer varchar2(50), producedate date, primary key (id));
create table engine_pk ( id number(10,0) not null, model varchar2(20), manufacturer varchar2(50), producedate date, primary key (id));
alter table engine_pk add constraint fk_engine_car_pk foreign key (id) references car_pk(id); 外键＋唯一约束create table car_fk ( id number(10,0) not null, name varchar2(15) not null, serial varchar2(30) not null, manufacturer varchar2(50) not null, producedate date, primary key (id));
create table engine_fk ( id number(10,0) not null, model varchar2(20) not null, manufacturer varchar2(50) not null, producedate date, carid number(10,0) unique, primary key (id));
alter table engine_fk add constraint fk_engine_car_fk foreign key (carid) references car_fk(id); 实体对象：在内存中有id属性的值对象：没有id的，依赖其他对象存在
一对多关系 一的一方保存多一方的一个集合，最好使用set，保证无重复元素多的一方保存一一方的一个对象的引用public class order implements Serializable{ private int id; private String owner; private String phone; private String address; private Set<Item> items = new HashSet<Item>();}public class Item implements Serializable{ private int id; private String product; private int amount; private order order; }
create table ec_item ( id number(10,0) not null, product varchar2(15) not null, amount number(10,0) not null, orderid number(10,0) not null, primary key (id));
create table ec_order ( id number(10,0) not null, owner varchar2(15) not null, phone varchar2(15) not null, address varchar2(50), primary key (id));
alter table ec_item add constraint fk_item_order foreign key (orderid) references ec_order(id); 多对多双方都保存对方的多个引用例子：学生选课public class TarenaCourse implements Serializable{ private int id; private String name; private int period; private Set<TarenaStudent> students = new HashSet<TarenaStudent>(); }public class TarenaStudent implements Serializable{ private int id; private String name; private Date birthday; private Set<TarenaCourse> courses = new HashSet<TarenaCourse>(); }
create table student ( id number(10,0) not null, name varchar2(15) not null, birthday date, primary key (id));
create table student_course ( sid number(10,0) not null, cid number(10,0) not null, primary key (sid, cid));
create table course ( id number(10,0) not null, name varchar2(15) not null, perion number(10,0), primary key (id));
alter table student_course add constraint fk_student foreign key (sid) references student(id);
alter table student_course add constraint fk_course foreign key (cid) references course(id);
通过学生姓名找课程 select c.name from cource c,student s,student_course scwhere c.id=sc.cid and s.id=sc.sid and s.name = 's1'
三、继承关系 public abstract class Computer implements Serializable{ private int id; private int price; private String manufacturer;}
public class Desktop extends Computer{ private boolean isLCD; }
public class Notepad extends Computer{ private float weight; private float thickness; }
１、建３张表 table per class子类中保存父类的主键作为外键create table computer_tpc ( id number(10,0) not null, price number(10,0) not null, manufacturer varchar2(30) not null, primary key (id));
create table desktop_tpc ( computerid number(10,0) not null, islcd char(1), primary key (computerid));
create table notepad_tpc ( computerid number(10,0) not null, weight float, thickness float, primary key (computerid));
alter table desktop_tpc add constraint fk_desk_computer_tpc foreign key (computerid) references computer_tpc(id);
alter table notepad_tpc add constraint fk_note_computer_tpc foreign key (computerid) references computer_tpc(id);
查找所有电脑的配制（只要是电脑就能被查出来） select c.id,c.price,d.islcd,n.weight,n.thicknessfrom computer c, desktop d,notepad nwhere c.id = d.computerid(+)and c.id = n.computer(+) ２、建２张表 create table desktop ( id number(10,0) not null, price number(10,0) not null, manufacturer varchar2(30) not null, islcd char(1), primary key (id));
create table notepad ( id number(10,0) not null, price number(10,0) not null, manufacturer varchar2(30) not null, weight float, thickness float, primary key (id));
３、建１张表create table computer_tph ( id number(10,0) not null, category char(1) not null, price number(10,0) not null, manufacturer varchar2(30) not null, islcd char(1), weight float, thickness float, primary key (id));
