数据库手动设置数据约束
1手动添加[主键约束]pk_employees_empid
alter table employees add constraint pk_employees_empid primary key(empid)
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2手动为empname增加非空约束
alter table employees alter column empname varchar(50) not null
3手动为empname增加唯一键约束
alter table employees add constraint uq_employees_empname unique(empname)
go
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4删除唯一键约束
alter table employees drop constraint uq_employees_empname
5为性别增加默认约束,使默认值为男
alter table employees add constraint df_employees_empgender
default(1) for empgender
6为年龄增加检测约束 0-120含0和120
alter table employees add constraint ck_employees_empage
check(empage>=0 and empage
7为性别增加检查约束 非 男 即 女
alter table employees add constraint ck_employees_empgender
check(empgender='男' or empgender='女')
8--为员工表增加外键约束
--首先，设置部门表中的depid为主键,并且外键不能为空
alter table department add constraint pk_deparment_depid primary key(depid)
alter table employee alter column depid int not null
alter table employee add constraint fk_employee_empdepid
foreign key(depid) references department(depid) on delete cascade
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9一条语句删除多个约束
alter table employees drop constraint fk_employees_empdepid,
ck_employees_empage,
uq_employees_empname
10一条语句为表增加多个约束
alter table employees add constraint
uq_employees_empname
unique(empname),
constraint
cksss
check(empage>=0and empage