oracle——数据表的相关操作——约束——各种约束详解

约束


1、主键约束 : primary key

select * from  student08;

create table student08 ( id number primary key,             /*创建主键约束*/
                         name varchar2(20),
                         sex varchar2(20),
                         age number,
                         address varchar2(20)
                    ) tablespace test
                    
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuan','nv',26,'jiang');    /*违反了主键唯一性约束*/

drop table student08;

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显性的为主键取别名


select * from  student08;

create table student08 ( id number constraint pk_student08 primary key,             /*创建主键约束*/
                         name varchar2(20),
                         sex varchar2(20),
                         age number,
                         address varchar2(20)
                    ) tablespace test
                    
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuan','nv',26,'jiang');    /*违反了主键唯一性约束*/

drop table student08;


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select * from  student08;

create table student08 ( id number,             /*创建主键约束*/
                         name varchar2(20),
                         sex varchar2(20),
                         age number,
                         address varchar2(20),
                         constraint pk_student08 primary key( id )
                    ) tablespace test
                    
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuan','nv',26,'jiang');                    
                    
drop table student08; 

----------------------------------------------------------------------------------------------------------------------------------

select * from  student08;

create table student08 ( id number,             /*创建主键约束*/
                         name varchar2(20),
                         sex varchar2(20),
                         age number,
                         address varchar2(20),
                         constraint pk_student08 primary key( id,name )
                    ) tablespace test
                    
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');
                    
insert into student08(id,name,sex,age,address) values(1,'yuanling01','nv',27,'zhejiang');

insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');                 

insert into student08(id,name,sex,age,address) values(1,'yuanling01','nv',27,'zhejiang');  
      
drop table student08;

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如果一个表创建时，并没有指定主键，那么在表创建之后，照样可以添加主键


select * from  student08;

create table student08 ( id number,
                         name varchar2(20),
                         sex varchar2(20),
                         age number,
                         address varchar2(20)
                    ) tablespace test
                    
修改列属性                    

---------   alter table student08 modify( id number primary key);  /*modify选项实际为修改列属性，并在修改列属性的同时，将该列指定为主键列*/

为表添加多列（而不是修改列属性）

alter table student08 add constraint pk_student08 primary key ( id,name );
                    
insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');
                    
insert into student08(id,name,sex,age,address) values(1,'yuanling01','nv',27,'zhejiang');

insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');                 
                    
drop table student08; 

删除主键：alter table student08 drop primary key;

利用删除约束的语法删除主键，因为表的约束可能有好多了，所以指定名称

alter table student08 drop constraint pk_student08;


+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
select * from  student08;

create table student08 ( id number,
                         name varchar2(20),
                         sex varchar2(20),
                         age number,
                         address varchar2(20)
                    ) tablespace test
                    

alter table student08 add constraint pk_student08 primary key ( id,name );

alter table student08 drop constraint pk_student08;



++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


禁用/启用 修改主键名 主键约束


select * from  student08;

create table student08 ( id number constraint pk_student08 primary key,             /*创建主键约束*/
                         name varchar2(20),
                         sex varchar2(20),
                         age number,
                         address varchar2(20)
                    ) tablespace test
                    
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');


alter table student08 disable primary key;

alter table student08 enable primary key;
                    
                    
insert into student08(id,name,sex,age,address) values(1,'yuan','nv',26,'jiang');    /*违反了主键唯一性约束*/

drop table student08;


alter table student08 rename constraint pk_student08 to zj;
alter table student08 rename constraint zj to pk_student08;



+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++



2、外键约束

























=======================================================================================================================
3、唯一性约束

select * from  student08;

create table student08 ( id number primary key,             /*创建主键约束*/
                         name varchar2(20) unique,             /*创建唯一性约束*/
                         sex varchar2(20),
                         age number,
                         address varchar2(20)
                    ) tablespace test

insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');


insert into student08(id,name,sex,age,address) values(2,'yuanling','nan',20,'jiangsu');  /*违反了name设置的唯一性*/


insert into student08(id,name,sex,age,address) values(2,'yuanling01','nan',20,'jiangsu');

insert into student08(id,name,sex,age,address) values(3,'','nan',25,'jiangsu');

insert into student08(id,name,sex,age,address) values(4,'','nan',28,'jiangsu09');

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


已经存在的表中添加唯一性约束

注意：与主键不同，一个唯一性约束只能建立在一个列上，因此，小括号内的列名只能有一个，不能是多个列名的列表；

要想在多个列上建立唯一性约束，只能针对每一个列分别创建；


select * from  student08;

create table student08 ( id number primary key,             /*创建主键约束*/
                         name varchar2(20),             /*创建唯一性约束*/
                         sex varchar2(20),
                         age number,
                         address varchar2(20)
                    ) tablespace test
----------------------------------------------------------------------------------------------
新建一个唯一性约束：

alter table student08 add constraint wyxys unique ( name );


重命名唯一性约束：

alter table student08 rename constraint wyxys to wyx_ys;

alter table student08 rename constraint wyx_ys to wyxys;


禁用唯一性约束：

alter table student08 disable constraint wyxys;

或者

alter table student08 modify constraint wyxys enable;


启用唯一性约束：

alter table student08 enable constraint wyxys;

删除唯一性约束：

alter table student08 drop constraint wyxys;
---------------------------------------------------------------------------

select * from student08;

insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');


insert into student08(id,name,sex,age,address) values(2,'yuanling','nan',20,'jiangsu');  /*违反了name设置的唯一性*/


insert into student08(id,name,sex,age,address) values(2,'yuanling01','nan',20,'jiangsu');

insert into student08(id,name,sex,age,address) values(3,'','nan',25,'jiangsu');

insert into student08(id,name,sex,age,address) values(4,'','nan',28,'jiangsu09');

=======================================================================================================================================
















4、检查约束

select * from  student08;

drop table student08;

create table student08 ( id number primary key,             /*创建主键约束*/
                         name varchar2(20),             /*创建唯一性约束*/
                         sex varchar2(20),
                         age number,
                         address varchar2(20),
                         constraint chk_age check ( age between 20and 50)
                    ) tablespace test


insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',27,'zhejiang');

insert into student08(id,name,sex,age,address) values(2,'yuanling','nan',50,'jiangsu'); 
 
insert into student08(id,name,sex,age,address) values(3,'yuanling','nan',19,'jiangsu');  

insert into student08(id,name,sex,age,address) values(4,'yuanling','nan',51,'jiangsu');  


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create table employees ( id number primary key,
                         name varchar2(50),
                         grade varchar2(50),
                         salary number,
                         constraint chk_salary check ( grade in ('manager','leader','staff') and ( grade = 'manager' and salary <= 8000 or grade = 'leader' and salary <= 5000 or grade = 'staff' and salary <= 4000 ))
                       ) tablespace test

select * from employees;

insert into employees( id,name,grade,salary) values (1,'shen','manager',7800);

insert into employees( id,name,grade,salary) values (2,'zhou','leader',4800);

insert into employees( id,name,grade,salary) values (3,'yuan','staff',3200);


插入非法数据：
insert into employees( id,name,grade,salary) values (4,'ling','staff',5000);


----------------------------

重新命名约束：

alter table employees rename constraint chk_salary to cksy;

alter table employees rename constraint cksy to chk_salary;


禁用约束：


alter table employees disable constraint chk_salary;
或者
alter table employees modify constraint chk_salary disable;



启用约束：

alter table employees enable constraint chk_salary;
或者
alter table employees modify constraint chk_salary enable;

删除约束：

alter table employees drop constraint chk_salary;


重新添加约束：

alter table employees add constraint chk_salary check ( grade in ('manager','leader','staff') and ( grade = 'manager' and salary <= 8000 or grade = 'leader' and salary <= 5000 or grade = 'staff' and salary <= 4000 ));


===========================================================================================================================================================================================================================================




























5、默认值约束

select * from  student08;

drop table student08;

create table student08 ( id number,             /*创建主键约束*/
                         name varchar2(20),             /*创建唯一性约束*/
                         sex varchar2(20),
                         age number default 22,
                         address varchar2(20) default 'abc'
                    ) tablespace test

insert into student08(id,name,sex,age,address) values(1,'yuanling','nv',20,'jiangsu');

insert into student08(id,name,sex) values(2,'shen','nan');
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使用函数作为默认值

create table sx ( id number,
                  name varchar2(50),
                  xssj date default sysdate
                 ) tablespace test

select * from sx;

insert into sx (id,name) values (1,'sww');

---------------------------------------------------------------

create table sx02 ( id number,
                  name varchar2(50),
                  xssj date
                 ) tablespace test

select * from sx02;


添加默认值约束：

alter table sx02 modify xssj default sysdate;

insert into sx02 (id,name) values (1,'sww');
---------------------------------------------------
alter table sx02 modify name default 'abc';

insert into sx02 (id) values (2);


修改默认值：

alter table sx02 modify name default '2wsdc';

insert into sx02 (id) values (3);


删除默认值：

alter table sx02 modify name varchar2(50) default null;

insert into sx02 (id) values (8);
































6、非空约束( not null )


create table sx03 ( id number,
                    name varchar2(50),
                    sex varchar2(10) not null
                 ) tablespace test

select * from sx03;

insert into sx03 (id,name) values (1,'sww');

insert into sx03 (id,name,sex) values (1,'sww','nv');

删除非空约束后，可以向表中插入数据（只需要把表的指定列的属性修改为null即可）

alter table sx03 modify ( sex null);

insert into sx03 (id,name) values (2,'123ew2');
----------------------------------------------------------------------
为已经存在的表，增加非空约束

create table sx04 ( id number,
                    name varchar2(50),
                    sex varchar2(10)
                 ) tablespace test

select * from sx04;



insert into sx04 (id,name,sex) values (1,'sww','nv');


alter table sx04 modify ( sex not null);

insert into sx04 (id,name,sex) values (2,'edcx','nan');

insert into sx04 (id,name) values (1,'sww');