Oracle中主键、外键、索引、序列、唯一性约束的创建

1、主键的创建

方法一：直接在sql语句中声明字段主键约束

create table table_name (id type[length]
constraint pk_name primary key,name tyoe[length],age type[length],class_id);

方法二：alter更改表添加约束

alter table table_name add constraint pk_name primary key (字段);

删除：

alter table table_name drop constraint contraint_name;

2、外键的创建

方法一：直接在sql语句中声明

create table table_name
(id type[length] primary key table_name_pk,name tyoe[length],age type[length],

class_id,foreign key (class_id) references table2_name(class_id));//字段类型要一致

方法二：alter更改表添加约束

alter table table_name add constraint fk_name foreign key(class_id) references table2_name(class_id);

删除：

alter table table_name drop constraint constraint_name;

3、索引的创建

create index index_name on table_name(字段);

删除：drop index index_name;

4、序列的创建

create sequence sequence_name

start with 1

increment by 1

nomaxvalue

nocycle；

删除：drop sequence sequence_name;

5、唯一性约束的创建

create table table_name(id
type[length],name type[length],

num type[length]
constraint constraint_name unique,class_id type[length]);

alter table add constraint constraint_name unique(一个或多个字段);