设教学数据库中有4 个关系: 教师关系T(T#, TNAME,TITLE) 课程关系C(C#,CNAME,T#) 学生关系S(S#,SNAME, AGE, SEX) 选课关系SC(S#,C#,SCORE) 现在教学数据库中的基本表SC上建立一个视图: CREATE VIEW S_SCORE(S#, C_NUM, AVG_SCORE) AS SELECT S#, COUNT(C#), AVG(SCORE) FROM SC GROUP BY S#; 试判断下列查询和更新操作是否允许执行。如允许,写出转换到基本表SC上的相应操作。 1SELECT * FROM S_SCORE; 2SELECT S#, C_NUM FROM S_SCORE WHERE AVG_SCORE>80; 3SELECT S#, A VG_SCORE FROM S_SCORE WHERE C_NUM >(SELECT C_NUM FROM S_SCORE WHERE S#='S4'); 4UPDATE S_SCORE SET C_NUM = C_NUM + 2 WHERE S#='S4'; 5DELETE FROM S_SCORE WHERE C_NUM>4;