有一个[学生课程]数据库，数据库中包括三个表：

1
create table student(
sno varchar(5) not null primary key,
sname varchar(10),
ssex char(2),
sage int,
sdept varchar(20))
 
2
alter table student add scome datetime
 
3
select sno,grade from sg where cno=5 order by grade desc
 
4
select max(grade) as 最高成绩,avg(grade) as 平均成绩 from sg where cno=1
 
5
delete from student where sno='05019'

1
create table Student(
Sno char(10) not null primary key,
Sname varchar(12),
Ssex char(1),
Sage int ,
Sdept char(20))
2
alter table student add column Scome datetime;
3
select Sno, Grade
from SG
where Cno='3'
order by grade desc
4
select max(grade), avg(grade)
from SG
where Cno='1'
5
delete from SG where Sno='05019'
delete from student where Sno='05019'