mysql学习——4,完整性约束
 
主键
create table feng(
teamno int not null,
playerno int not null,
division char(6) not null,
primary key(teamno)
)


create table feng(

teamno int not null primary key ,
playerno int not null,
division char(6) not null,
)

 

 
复合主键
create table feng(
teamno int not null,
playerno int not null,
division char(6) not null,
primary key(teamno,playerno)
)

 

 
替代键(候选键)
 
create table feng(
teamno int not null primary key ,
playerno int not null,
division char(6) not null,
unique(playerno)
)

create table feng(
teamno int not null primary key ,
playerno int not null,
division char(6) not null,
unique(playerno,division)
)

 

 
外键(在innoDB中使用)
外键声明包括三个部分
1,那个列或列组合是外键
2,指定外键参照的表和列
3,参照动作[cascade(级联操作),restrict(拒绝操作),set null(设为空),no action,set default]
如果没有指定参照动作默认是
on update restrict
on delete  restrict
create table feng(
teamno int not null primary key ,
playerno int not null,
division char(6) not null,
foreign key(division)
references othertable   (column)
on update restrict
unique(playerno)
)

check完整性约束
create  table players 
(playerno int not null,
 sex   char(1) not null,
         check (sex in ('m','f'))
)

create  table players 
(playerno int not null,
birth_date  date,
 sex   char(1) not null,
         check (sex in ('m','f'))
joined smallint not null,
             check (year(birth_date)<joined),
             check (joined<1880),
)

create  table players 
(playerno int not null,
birth_date  date,
 sex   char(1) not null,
          check (sex in (select sex from wholetab)
)