添加约束_为地址字段定义默认约束为

添加约束
--在stuInfo表中添加约束，将stuNo作为主键，pk_stuNo为约束名
alter table stuInfo
add constraint pk_stuNo primary key(stuNo)

--在stuInfo表中添加唯一约束，stuID代表添加约束的列名，uq_stuID为约束名
alter table stuInfo
add constraint uq_stuID unique(stuID)

--在stuInfo表中添加默认约束，stuAddress列的默认值为('地址不详')，df_stuAddress为约束名
alter table stuInfo
add constraint df_stuAddress default('地址不详') for stuAddress

--在stuInfo表中添加检查约束，stuAge>15 and stuAge<40，ck_stuAge为约束名
alter table stuInfo
add constraint ck_stuAge check(stuAge between 15 and 40)

--在stuMarks表中添加外键约束，foregin key(stuNo)建立外键，references stuInfo (stuNo)建立主键
alter table stuMarks
add constraint fk_stuNo foregin key(stuNo) references stuInfo (stuNo)

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