Mysql database learning-4, integrity constraints

Mysql database learning-4, integrity constraints primary key

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,)

 

Composite primary key

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

 

Alternative key (candidate key)

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))

 

The foreign key statement (used in innoDB) consists of three parts: 1. The column or column combination is foreign key 2, and the table and column 3 referenced by the foreign key are specified, reference action [cascade (cascade operation), restrict (reject operation), set null (set to null), no action, set default] If no reference action is specified, the default action is

On update restricton delete restrictcreate 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 restrictunique (playerno) check Integrity Constraint 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 ))