题1

https://www.nowcoder.com/practice/203d0aed8928429a8978185d9a03babc?tpId=240&tags=&title=&difficulty=0&judgeStatus=0&rp=0

解1

(select exam_id as tid,count(distinct uid) as uv,count(exam_id) as pv
FROMexam_record
group byexam_id)union all # 不去重(select question_id as tid,count(distinct uid) as uv,count(question_id) as pv
FROMpractice_record
group byquestion_id)order  BYLEFT(tid, 1) desc,uv desc,pv DESC;

解2

select *
from(select exam_id as tid,count(distinct uid) as uv,count(*) as pvfrom exam_recordgroup by exam_idorder by uv desc, pv desc) as examunionselect *
from(select question_id as tid,count(distinct uid) as uv,count(*) as pvfrom practice_recordgroup by question_idorder by uv desc, pv desc) as practice # 注意子表必须有表名。

解3

用tid字段的左边第一个数来排序。

要注意的是关于UNION后的排序问题，要么在UNION之前分别单独排序（如上解法），要么在union之后再排序：

(SELECT exam_id AS tid, COUNT(DISTINCT exam_record.uid) uv,COUNT(*) pv
FROM exam_record
GROUP BY exam_id)UNION(SELECT question_id AS tid, COUNT(DISTINCT practice_record.uid) uv,COUNT(*) pv
FROM practice_record
GROUP BY question_id)ORDER BY LEFT(tid,1) DESC, uv DESC, pv DESC;

题2

https://www.nowcoder.com/practice/a126cea91d7045e399b8ecdcadfb326f?tpId=240&tags=&title=&difficulty=0&judgeStatus=0&rp=0

select uid,'activity1' as activity
from exam_record
where year(submit_time) = 2021
group by uid
having min(score) >= 85 # 对于每组 要求最小得分不小于85，过滤union all  # 将两个筛选合并。不去重select distinct uid,'activity2' as activity
from exam_record e_r join examination_info e_ion e_r.exam_id = e_i.exam_id
where year(e_r.submit_time) = 2021and e_i.difficulty = 'hard'and e_r.score > 80and timestampdiff(minute, e_r.start_time, e_r.submit_time) * 2 < e_i.duration
order by uid

或：

select uid,'activity1' as activity
from exam_record
where year(submit_time) = 2021
group by uid
having min(score) >= 85 # 对于每组 要求最小得分不小于85，过滤union all  # 将两个筛选合并。不去重select distinct uid,'activity2' as activity
from exam_record e_r join examination_info e_ion e_r.exam_id = e_i.exam_id
where year(submit_time) = 2021and difficulty = 'hard'and score > 80and timestampdiff(minute, start_time, submit_time) * 2 < duration
order by uid

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sql多表查询之合并查询（union）

题1

解1

解2

解3

题2

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