分享一个题，请大神给我讲解一下，有关于pl／sql的，下面发代码截图和代码9、按各科平均成绩从低到高和及格率的百分数从高到低顺序及格率：大于60分的人数/总人数（选课总人数）--SELECT * FROM STUDENT;--SELECT * FROM TEACHER;--SELECT * FROM COURSE;--SELECT * FROM SC;SELECT AVG(SCORE) FROM SC GROUP BY CNO;--各科平均成绩SELECT COUNT(SCORE) FROM SC WHERE SCORE>60 GROUP BY CNO;--各科大于六十分的人数SELECT COUNT(SNO) FROM SC GROUP BY CNO;--各科总人数SELECT COUNT('1') / COUNT('2') "及格率" FROM SC WHERE '1' IN (SELECT COUNT(SCORE) FROM SC WHERE SCORE > 60 GROUP BY CNO) AND '2' IN (SELECT COUNT(SNO) FROM SC GROUP BY CNO); --及格率(报错,除数为零)SELECT SC.*, '及格率' FROM SC ORDER BY (SELECT AVG(SCORE) FROM SC GROUP BY CNO), (SELECT COUNT('1') / COUNT('2') "及格率" FROM SC WHERE '1' IN (SELECT COUNT(SCORE) FROM SC WHERE SCORE > 60 GROUP BY CNO) AND '2' IN (SELECT COUNT(SNO) FROM SC GROUP BY CNO)) DESC;