表内容的增加操作：
insert into student values ('1','小明')
表内容的修改操作：
update student set sname = 'djdjdj' where sno = '1'
表内容的删除操作：
delete from student where sno = '1'
表内容的增加操作：
insert into student values ('1','小明')
表内容的修改操作：
update student set sname = 'djdjdj' where sno = '1'
表内容的删除操作：
delete from student where sno = '1'