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【多选题】查询至少选修了学生201215122选修的全部课程的学生号码,以下说法正确的有( )
A.
查询学号为x的学生，对所有的课程y，只要201215122学生选修了课程y，则x也选修了y。即不存在学生201215122选修的课程y，学生x没有选
B.
该查询只需要在SC表中进行，因此需要用自身连接，通过别名以示区别
C.
SELECT DISTINCT Sno FROM SC S1 WHERE NOT EXISTS ( SELECT cno FROM SC S2 WHERE S2.Sno = '201215122 ' AND cno not in (SELECT cno FROM SC S3 WHERE S3.Sno=S1.Sno AND S3.Cno=S2.Cno) )
D.
SELECT DISTINCT Sno FROM SC S1 WHERE NOT EXISTS ( SELECT cno FROM SC S2 WHERE S2.Sno = ' 201215122 ' AND not EXISTS (SELECT * FROM SC S3 WHERE S3.Sno=S1.Sno AND S3.Cno=S2.Cno) )；