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【简答题】
数据库中表关系如下: Student(S#,Sname,Sage,Ssex) 学生表 Course(C#,Cname,T#) 课程表 SC(S#,C#,score) 成绩表 Teacher(T#,Tname) 教师表 请编写SQL实现解决以下问题: 1、查询平均成绩大于60分的同学的和平均成绩; 2、查询所有同学的、姓名、选课数、总成绩; 3、查询姓“”的老师的个数; 4、查询各科成绩前三名的记录:(不考虑成绩并列情况) 5、删除学习“”老师课的SC表记录;
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