Oracle学习笔记2

• 主键

create table userinfo_test(
userid number(3,0),
username varchar2(20),
pwd varchar2(20),
constraint pk_id_name primary key(userid,username)
);

select constraint_name from user_constraints a where a.TABLE_NAME='USERINFO_TEST'; 

alter table table_name add constraint pk_id primary key(id);--修改表时添加外键约束
alter table rename constraint old_name to new_name;  --更改约束的名称
alter table disable|enable constraint constraint_name; --禁用或启用约束名称
alter table drop constraint constraint constraint_name;--删除约束
alter talbe drop primary key[cascade];--删除主键

• 外键

create table table_name(
...
column datatype references table1(primary_key_column);
...
);----设置外键依赖

constraint constraint_name foreign key(column_name) references table_name(column_name) [on delete cascade];

add constraint constraint_name foreign key(column_name) references table_name(column_name) [on delete cascade];--修改表时添加外键约束

alter table disable|enable constraint constraint_name;--禁用启用外键约束
alter table drop constraint constraint_name;--删除外键约束