基于"学生-选课-课程"数据库中的三个关系： S（S#，SNAME，SEX，BIRTHYEAR，DEPT），主码为S# C（C#，CNAME，TEACHER），主码为C# SC（S#，C#，GRADE），主码为（S#，C#） 查找"由王建老师执教的操作系统课程的平均成绩、最高成绩和最低成绩"，正确的SQL语句是
- A.SELECT AVG(GRADE), MAX(GRADE), MIN(GRADE) FROM C, SC GROUP BY CNAME = "操作系统" AND TEACHER = "王建"
- B.SELECT AVG(GRADE), MAX(GRADE), MIN(GRADE) FROM C, SC WHERE CNAME = "操作系统" AND TEACHER = "王建" AND SC.C# = C.C#
- C.SELECT AVG(GRADE), MAX(GRADE), MIN(GRADE) FROM C, SC HAVING CNAME = "操作系统" AND TEACHER = "王建" AND SC.C# = C.C#
- D.SELECT AVG(GRADE), MAX(GRADE), MIN(GRADE) FROM C, SC HAVING CNAME = "操作系统" AND TEACHER = "王建"
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参考答案：B
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