返回身份证号相同，但性别不同的信息
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select A.name,A.people_id from
(select name,people_id,count(distinct sex) as 'count' from people group by name,people_id) as A
where A.count= 2;
将查询出的两列数据 合并成一列 并去重。表明为union_1
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select nid from union_1
union
select mid from union_1
用mysql语句实现 右边那样的结果
SELECT a.ver,a.kid,a.mid FROM top3 a
inner join top3 b on a.ver =b.ver and a.kid=b.kid and a.mid<=b.mid
group by a.ver,a.kid,a.mid having count(*)<=3
order by a.ver, a.kid desc, a.mid desc;
查询两门及两门以上不及格同学的平均分
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select name,avg(score),sum(score<60)as gk from stu
group by name having gk>=2;
