–constraint
–not null 非空约束
create table demo01(
empno number(4),
ename varchar2(10) not null,
job varchar2(10)
)
insert into demo01 values(1234,’ ‘,’sales’);
select * from demo01;
–unique 唯一键
create table demo02(
empno number(4) unique,
ename varchar2(10),
job varchar2(8)
)
select * from demo02;
insert into demo02 values(1234,’zhangsan’,’sales’);
insert into demo02 values(1234,’lisi’,’sales’);
insert into demo02 values(null,’wangwu’,’sales’);
insert into demo02 values(null,’zhaoliu’,’sales’);
–非空&唯一
create table demo03(
empno number(4) not null unique,
ename varchar2(10),
job varchar2(8)
)
insert into demo03 values(1234,’zhangsan’,’sales’);
insert into demo03 values(null,’lisi’,’sales’);
–自定义检查约束
create table demo04(
empno number(4),
ename varchar2(10),
job varchar2(8),
age number(3) check(age>0 and age<200),
gender varchar2(3) check(gender=’男’ or gender=’女’)
)
insert into demo04 values(1234,’zhangsan’,’sales’,56,’男’)
insert into demo04 values(1234,’zhangsan’,’sales’,44,’详’)
–创建约束时，为约束起名 constraint
create table demo05(
empno number(4),
ename varchar2(10),
job varchar2(8),
age number(3) constraint ck_age check(age>0 and age<200)
)
insert into demo05 values(1234,’zhangsan’,’sales’,300);
–在添加完列后，还可以添加约束
–除了not null不可以
create table demo06(
empno number(4),
ename varchar2(10),
age number(3),
constraint uq_empno unique(empno),
constraint ck_age2 check(age>0 and age<200)
)
insert into demo06 values(1234,’zhangsan’);
insert into demo06 values(1234,’lisi’);
–主键约束
–为了保证该列的数据能够证明行记录在表中是唯一的
–主键约束从形式看，类同于（非空和唯一）约束
create table demo07(
empno number(4) primary key,
ename varchar2(10),
age number(3)
)
insert into demo07 values(1234,’zhangsan’,18);
insert into demo07 values(1234,’lisi’,18);
insert into demo07 values(null,’wangwu’,20);
–在列之后添加
create table demo08(
empno number(4),
ename varchar2(10),
age number(3),
constraint pk_empno primary key(empno)
)
— 一张表只有一个主键
create table demo09(
empno number(4) primary key,
ename varchar2(10) primary key,
age number(3)
–constraint pk_empno primary key(empno)
)
— 一张表虽然只有一个主键，但可以选择多个列，作为联合主键
create table demo09(
empno number(4) ,
ename varchar2(10),
age number(3),
constraint pk_empno2 primary key(empno,ename)
)
insert into demo09 values(1234,’zhangsan’,18);
insert into demo09 values(1234,’lisi’,20);
insert into demo09 values(2345,’zhangsan’,20);
insert into demo09 values(1234,null,18);
–外键foreign key
–外键用来描述两张表之间的关系，必须保证外键列的值必须为参考列的值中的一个
create table t_class(
classid number(2) primary key,
classname varchar2(20) not null,
classnum varchar2(30)
)
insert into t_class values(10, ‘java班’,’教室6′);
insert into t_class values(20, ‘大数据班’,’教室3′);
insert into t_class values(30, ‘python班’,’教室4′);
delete from t_class where classid = 20;
create table t_student(
stuid number(8) primary key,
stuname varchar2(30) not null,
stuphone varchar2(11),
classid varchar2(2) references t_class(classnum)
)
insert into t_student values(11111111,’方子恒’,110,10);
insert into t_student values(11111112,’马子明’,120,20);
insert into t_student values(11111113,’王福禄’,130,10);
select * from t_class;
select * from t_student;
–存在外键的表为从表，被依赖的表为主表
–外键不一定为主表的主键，也可以为主表的唯一键
–约束除了在建表时，可以添加约束外，还可以修改表时修改约束
alter table demo07 add constraint uq_demo07_ename unique(ename);
alter table demo07 drop constraint uq_demo07_ename
–索引：
create index idx_emp_ename_job on emp(ename,job)
select * from emp where ename = ‘smith’ and job= ‘xxx’;
–只有添加索引的列，通过该列进行查询时，速度才可以变快
create table demo110(
id number(5) primary key,
name varchar2(20) not null,
nickname varchar2(30) unique
)