摘要： 1查询刘伟选的课程名。(t,tc,c)select distinct cn from t,tc,cwhere t.tno=tc.tno and tc.cno=c.cno andc.cno in(select tc.cno from tcwhere tc.tno in(select t.tno from t where tn='刘伟'))2查询不学数据库的学生学号。(sc,c)select sno from swhere not exists (select * from cwhere cn='数据库' andexists (select * from scwhe 阅读全文