sql添加主键外键

在创建表时设立主键

mysql

create table student(

sid integer,

sname nvarchar2(64),

primary key(sid)

)

oracle,sql server

create table student(

sid integer primary key,

sname nvarchar2(64),

)

给已存在的表添加主键

mysql,oracle,sql server

alter table student add primary key(sid);

注意：再用alter table 添加主键之前要保证要设立主键的列not null

在创建表时设立外键

mysql

create table teacher(

tid integer,

tname varchar(64),

primary key(tid)

)

create table student(

sid integer,

sname nvarchar2(64),

teacherId integer,

primary key(sid),

foreign key(teacherId) references teacher(tid)

)

oracle,sql server

create table student(

sid integer primary key,

sname nvarchar2(64),

teacherId integer references teacher(tid)

)

给已存在的表添加主键

mysql,sql server

alter table student add foreign key(teacherId) references teacher(tid);

oracle

alter table student add(constraint fk_tid) foreign key(teacherId) reference teacher(tid);