oracle嵌套表示例
----嵌套表：就是把一个表中的字段定义为一个表，这个字段表的数据存储在外部的一个表中，
例如下例嵌套表中的数据存储在required_tab表中。
----嵌套表可以有效地代替多个表之间的连接
create type bookobj as object(
title varchar2(40),
author varchar2(40),
catalog_number number(4)
);
/
create type booklist as table of bookobj; -----------定义一个嵌套表，该表可以被嵌套在其他表中，他的字段就是bookobj中的字段
/
create table course_material(
department char(3),
course number(3),
required_reading booklist -----在表中再定义一个表，即booklist表，他就是嵌套在course_material中的表，也就是嵌套表。
------他和主表course_material之间是主从关系，即一条主表记录对应一个嵌套表中的多条记录。
) nested table required_reading store as required_tab;
/
-----------------------给表和嵌套表输入值，commit后被提交到数据库里保存
declare
v_books booklist:=booklist(bookobj('ssss','www',444));-------定义一个booklist类型的嵌套表变量v_books，并给出初值。
begin
insert into course_material values('cs',101,booklist(bookobj('www','bbb',1),bookobj('aa','dd',33)));
insert into course_material values('his',301,v_books);
end;
或单独插入一条记录：
insert into course_material values('ss',102,booklist(bookobj('w','b',1),bookobj('a','d',3)));
-----------------------更新嵌套表操作，即将required_reading作为一个字段
declare
v_books booklist:=booklist(bookobj('xyz','bbb',111),bookobj('zq','ccc',222));
begin
update course_material
set required_reading = v_books
where department = 'his' and course = 301;
end;
----执行结果为子记录全部被删除，新添加两个bookobj记录
-------------删除嵌套表中的记录
delete from course_material where department = 'his';----对应主表his的嵌套表中的记录将被删除
＝＝＝＝＝＝＝＝＝＝＝＝＝直接对嵌套表进行插入＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
insert into the(select required_reading from course_material where department='his' )
values('gog','ggg',999)
-----上面红色的表示一个表，注意前面必须加上the，表示是嵌套表。
＝＝＝＝＝＝＝＝＝＝＝＝＝直接对嵌套表进行更新＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
update the(select required_reading from course_material where department='his' )
set catalog_number = catalog_number + 10 -----对嵌套表中的字段进行操作
where catalog_number = 111;
＝＝＝＝＝＝＝＝＝＝＝＝＝直接对嵌套表进行删除＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝
delete from the(select required_reading from course_material where department='his' )
where catalog_number = 111;
=========================直接进行嵌套表的查询，只能返回主表的一条记录的子表，即如果course_material返回多于2条的记录则报错
select * from the(select required_reading from course_material where department='his');
或
select * from the(select required_reading from course_material where department='his') where catalog_number=999
报错：select * from the(select required_reading from course_material where department in ('his','www'))