摘要： 1查询出只选修了一门课程的全部学生的学号和姓名最初想法是select count(*)然后再去比较count(*),要是必就不会了select s_id ,sname from student,sc where sc.s_id=student.idgroup by sc.s_id,sname having count(*)=1;2查询同名同性学生名单，并统计同名人数开始是让sc的2个表来比较同名的，然后发现错了多比了几遍，然后又想把id也相同。但是错的更离谱select sname count(sname) from student group by id having count(sname 阅读全文

摘要： 查询各科成绩前三名的记录:(不考虑成绩并列情况)sc表，student表，course表比如某一科的前三名selcet score ,c_id from sc where c_id=1 order by score limit0,3;于是select from sc as s1 where s1.score in(select score from sc where s1.c_id=c_id group by c_id order by score desc limit0,3);但是这个出了问题，limit 不能有in，看网上说法可以再套一个select，但是有个问题是s1.c_id不认识.. 阅读全文