oracleѧϰ£¨´´½¨±í£©

ÎÒÏë×î³õѧϰÊý¾Ý¿âʱ¶¼ÊÇÒÔstudent±í¡¢course±íºÍsc±íΪÀýµÄ°É
Ê×ÏÈ´´½¨ÕâÈýÕÅ±í£º±ØҪʱ¿ÉÖØд´½¨Óû§¼°ÃÜÂë²¢µÇ½
»·¾³£ºoracle 10g
declare
  vcnt number;
begin
  select count(*) into vcnt from user_tables where table_name='SC';
  If vcnt = 1 Then
    Execute immediate 'drop table sc';
  end if;
  select count(*) into vcnt from user_tables where table_name='STUDENT';
  If vcnt = 1 Then
    Execute immediate 'drop table student';
  end if;
  select count(*) into vcnt from user_tables where table_name='COURSE';
  If vcnt = 1 Then
    Execute immediate 'drop table course';
  end if;
end;
/
--´´½¨±í
Create table student
(sno char(10) primary key,
 sname varchar(20) not null,
 sage smallint,
 ssex char(2),
 sdept varchar(20));
Create table course
(cno char(10) primary key,
 cname varchar(20) not null,
 credit smallint);
Create table sc
(sno char(10),
 cno char(10),
 grade smallint,
 primary key(sno,cno));
--Ïò±íÖвåÈëÊý¾Ý
insert into student values('001','¸ðÁé','19','f','MA');
insert into student values('002','ÔÀÁÖÔÂ','25','f','MA');
insert into student values('003','¼§Ê¤¿¡','16','f','CS');
insert into student values('004','ÂíÔ´','20','f','MA');
insert into student values('005','ÎÌÓ¡','23','m','C');
insert into course values('C01','CÓïÑÔ','4');
insert into course values('C02','Êýѧ','4');
insert into course values('C03','Ó¢Óï','2');
insert into course values('C04','¼ÆËã»ú','5');
insert into course values('C05','Êý×Öµç·','3');
insert into course values('C06','Êý¾Ý¿â','2');
--001ºÅѧÉúÑ¡Ð޿γÌ
insert into sc values('001','C05','75');
insert into sc values('001','C01','68');
insert into sc values('001','C03','86');
insert into sc values('001','C02','40');
insert into sc values('001','C04','97');
--002ºÅѧÉúÑ¡Ð޿γÌ
insert into sc values('002','C01','60');
insert into sc values('002','