USE School
CREATE TABLE Stu_Union(sno CHAR(5) NOT NULL UNIQUE,
                       sname CHAR(8),
                       ssex CHAR(1),
                       sage INT,
                       sdept CHAR(20),
                       CONSTRAINT  PK_Stu_Union  PRIMARY KEY(sno) );   
insert Stu_Union values ( '10000','王敏','1',23,'CS');
UPDATE Stu_Union SET sno=''       WHERE sdept='CS';
UPDATE Stu_Union SET sno= '95002' WHERE sname='王敏';
select * from stu_union;