mysql數據庫學習——4，完整性約束

mysql資料庫學習——4，完整性約束

 

主鍵

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


create table feng(

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

 

 

復合主鍵

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

 

 

替代鍵（候選鍵）

 

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

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

 

 

外鍵（在innoDB中使用）

外鍵聲明包括三個部分

1，那個列或列組合是外鍵

2，指定外鍵參照的表和列

3，參照動作[cascade（級聯操作）,restrict（拒絕操作）,set null（設為空）,no action,set default]

如果沒有指定參照動作默認是

on update restrict
on delete  restrict
create table feng(
teamno int not null primary key ,
playerno int not null,
pision char(6) not null,
foreign key（pision）
references othertable   （column）
on update restrict
unique(playerno)
)

check完整性約束
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)
)