选择m表中的category，以及计算中位数决策时间并命名为median_decision_time

SELECT m.category, CAST( PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY TIMESTAMPDIFF(SECOND, a.time, d.time)) AS UNSIGNED ) AS median_decision_time FROM app a # 将app表与mapping_table表连接，根据package_name匹配 JOIN mapping_table m ON a.package_name = m.package_name # 用子查询查找每个用户下载每个应用的最早时间 JOIN ( SELECT userid, package_name, MIN(time) AS time FROM app WHERE action_type = 'download' GROUP BY userid, package_name ) AS d ON a.userid = d.userid AND a.package_name = d.package_name

选择action_type为itemShow的记录

WHERE a.action_type = 'itemShow'

按照category进行分组

GROUP BY m.category