DERIVEDTBL关键字的作用?
我在分组中遇到一个问题:
我有两个表格,一个学生student(sno,sname,sex,sage),一个选课表sc(sno,cno,grade),其中,sno为学号,cno为课程号,grade为成绩。下面我要查询女生的平均成绩,所用语句为:
SELECT AVG(Grade) AS Girl_Grade FROM
(SELECT Student.Sno, Sname, Cno, Grade, sex
FROM Student, SC
WHERE (Student.Sno = sc.Sno)) GROUP BY Sex
HAVING (sex = '女')
这条语句不对,提示group 附近有语法错误,但是如果这样加入DERIVEDTBL 就可以了,
SELECT AVG(Grade) AS Girl_Grade FROM
(SELECT Student.Sno, Sname, Cno, Grade, sex
FROM Student, SC
WHERE (Student.Sno = sc.Sno)) DERIVEDTBL GROUP BY Sex
HAVING (sex = '女')
请问DERIVEDTBL关键字的作用?
第二个问题:
SELECT AVG(Grade) AS Girl_Grade FROM
(SELECT Student.Sno, Sname, Cno, Grade, sex
FROM Student, SC
WHERE ((Student.Sno = sc.Sno) and sex = '女') )
这个语句不对,提示最后一个括号附近有错误,这是为什么?
谢谢!!