查詢至少選修了兩門課程的學生學號的sql語句

第一個：至少選修c1和c2的學生編號

           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'

 

第二個：同時選修c1和c2的學生編號

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