查询至少选修了两门课程的学生学号的sql语句

第一个：至少选修c1和c2的学生编号

           1.  select sno from sc where sc.cno='c1' and sno in(select sno from sc where cno='c2')

           2.select sno from sc scx,sc scy where scx.sno=scy.sno and scx.cno='c1' and scy.cno='c2'

 

第二个：同时选修c1和c2的学生编号

             select sc.sno from sc where sc.cno = 'c1' intersect select sc.sno from sc where sc.cno= 'c2';