Leetcode-sql-five

select play_id,min(event_date) as first_login
from activity
group by play_id;

select a.player_id, a.device_id from activity a
right join (select play_er, min(event_date) as latest_date
            from activity
            group by play_id) b   -- 将上面的结果作为表b
      on a.event_date = b.latest_date
      where a.player_id = b.play_id;

select a.play.id, a.device_id
from activity a
where (a.play_id, a.event_date) in (select play_id, min(event_date) as first_login
                                    from activity
                                    group by player_id);    --将子查询的结果作为条件，in关键字可以包含两个字段信息

select a.player, a.event_date, (select sum(b.games_played)   -- 	求和函数sum()
                                from activity b
                                where a.play_id=b.play_id
                                and a.event_date=b.event_date) as b "games_played_as_far"   -- 通过临时表筛选出此日期前的游戏总数
                                from activity as a;

select round((select count(distinct b.play_id)
             from activity as b, activity as c
             where b.event_date=(select min(temp.event_date)
                                from activity as temp.play_id=b.play_id)
              and b.play_id=play_id
              and datediff(b.event_date, c.event_date=-1)/count(distinct a.play_id), 2) as "fraction"
             from activity as a;