检查Logic Java 课程最近一次考试。如果全部没有通过考试（60分及格），则认为本次考试偏难，计算该次考试平均分加5分。
SELECT AVG(studentResult)+5 平均分 FROM result
如果子查询语句没有结果 则 返回 true
WHERE NOT EXISTS (
#查询Logic Java 最后一次考试成绩的纪录
SELECT * FROM result WHERE subjectno = (
SELECT subjectNo FROM SUBJECT WHERE subjectName = ‘Logic Java’
)AND examDate = (
SELECT MAX(examDate) FROM result WHERE subjectNO = (
SELECT subjectNo FROM SUBJECT
WHERE subjectName = ‘Logic Java’
)
# 成绩大于 60
)AND studentResult > 60)
查询 Logic Java 的编号
AND subjectNO = (SELECT subjectNO FROM SUBJECT
WHERE subjectName = ‘Logic Java’)
查询 Logic Java 最近的考试时间
AND examDate = (
SELECT MAX(examDate) FROM result WHERE subjectNo = (
SELECT subjectNO FROM SUBJECT
WHERE subjectName = ‘Logic Java’
)
)