rimary_name varchar(29),
constraint pk_test primary key(primary_id)
);
#删除主键约束
alter table test
drop primary key;
#使用表级语法增加主键约束
alter table test
add primary key(test_id ,test_name);
#使用列级约束语法增加主键约束
alter table test
modify test_name varchar(30) primary key;
------------------------------------------------------------------
#为了保证从表参照的主表存在，通常应该先建立主表
create table teacher_table(
#auto_increment
teacher_id int auto_increment,
teacher_name varchar(255),
primary key(teacher_id)
);
create table student_table(
student_id int auto_increment primary key,
student_name varchar(255),
#指定java_teacher参照到teacher_table的teacher_id的列
java_teacher int references teacher_table(teacher_id)
#java_teacher int
#foreign key(java_teacher) references teacher_table(teacher_id)
#constraint student_teacher_fk foreign key(java_teacher) references
teacher_table(teacher_id)
);
---------------------------------------------------------------------------------------------
#check约束
create table test(
test_id int auto_increment primary key,
test_age int not null,
check(test_age>0 and test_age<120)
)
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