编写SQL
create table student ( sno char(9) primary key, sname char(20) unique, ssex char(2), sage smallint, sdept char(20) ); create table course ( cno char(4) primary key, cname char(40), cpno char(4), ccredit smallint, foreign key(cpno) references course(cno) ); create table sc ( sno char(9), cno char(4), grade smallint, primary key(sno,cno), foreign key(sno) references student(sno), foreign key(cno) references course(cno) ); alter table student alter column sage int; alter table course add unique(cname); create unique index stusno on student(sno); create unique index coucno on course(cno); create unique index scno on sc(sno asc,cno desc); select sno,sname from student; select sname,sno,sdept from student; select * from student; select sname,2004-sage from student; select sname NAME,'year of birth:' BIRTH,2004-sage BIRTHDAY,lower(sdept) DEPARTMENT from student; select distinct sno NUMBER from sc; select sname NAME from student where sdept='cs'; select sname,sage from student where sage<20; select distinct sno from sc where grade<60; select sno from student where sno between 12436220 and 12436240; select sname,ssex from student where sdept in('cs','ma','is'); select sname,ssex from student where sdept not in('cs','ma','is'); select * from student where sno like '200215121'; select sno from student where sname like '刘%'; select sno from student where sname like '欧阳_'; select sno from student where sname in('刘%','欧阳_'); select sname from student where sname like '_阳%'; select sno from student where snamd not like '刘%'; select sname from student where sname like 'DB\_Design'escape'\'; select sno,cno from sc where grade is null; select sno,cno from sc where grade is not null;