oracle笔记 (创建、更改、删除[table,constraint,index,view,sequence])

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RIA
对表字段的修改

alter table stu add(addr varchar2(100));
ALTER TABLE STU DROP (ADDR)
alter table  stu modify (addr varchar(150));


对约束的修改

alter table stu drop constraint stu_class_fk;
alter table stu add constraint stu_class_fk foreign key (class) referencesclass(id);

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oracle_dictionariys
oracle数据字典表
oracle数据字典表的表
: dictionariy

desc dictionary;
select * from dictionary;
select table_name from dictionary where table_name like 'USER%' order by table_name;



uers_tables
--装的是当前用户的表
user_tables
--装的是当前用户的视图
user_constraints
--装的是当前用户的约束

--查看当前用户的所有表
select table_name from user_tables;
--查看当前用户的所有视图
select view_name from user_views;
--查看当前用户的所有约束条件
select constraint_name from user_constraints;

================================================================
索引(indexs)和视图(views)
建立索引
create index idx_stu_email on stu (email);
删除索引
drop index idx_stu_email;
查看索引
select index_name from user_indexes
访问量大(优化性能)才建索引,不要轻易建立索引;
视图
create view v$_stu as select id, name, age from stu;
=================================================================
sequence_and_review
oracle特有的 序列(sequence)
create table article
(
id number,
title varchar2(1024),
cont long
);

创建序列
create sequence seq;
插入使用序列
insert into article values (seq.nextval,'a','b');

一般一个sequence对应一个字段
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数据库常用对象
表
视图
约束
索引
序列