12 2021 档案

摘要：select count(*),round(avg(age),1) from (select user_id,age from log group by user_id,age) as a union all select count(*), round(avg(age),1) from( sele 阅读全文

摘要：1.时间格式转换 select DATE_FORMAT(regexp_replace(visit_date,'/','-'),'%Y-%m')from visitor; 2.计算每人单月访问量 select user_id,mn,sum(visit_count)as count from ( sel 阅读全文

摘要：1.先求出每个学科的平均成绩 SELECT user_id, subject_id, score, avg( score ) over ( PARTITION BY subject_id ) AS avg_score FROM student 2.每个学科的成绩与平均学科成绩比较，大于记为1，小于为 阅读全文

摘要：方式一： SELECT *FROM ( SELECT *, lead ( login_data, 2 ) over ( PARTITION BY user_id ORDER BY login_data ) AS rn FROM last_3days ) AS a WHERE datediff ( l 阅读全文