join 新表连接综训

对于较复杂的题，按需求处理产生新表，再连接。

力扣1126：

select business_id
from Events
join
    (select event_type,avg(occurences) as avg_occurences
    from Events
    group by event_type) as tmp
on Events.event_type = tmp.event_type
and Events.occurences > tmp.avg_occurences
group by business_id
having count(*) >= 2

力扣1212：

select Teams.team_id,team_name,sum(ifnull(points,0)) as num_points
from Teams left join 
    ((select host_team,
    case when host_goals > guest_goals then 3
        when host_goals = guest_goals then 1
        else 0 end as points
    from Matches)
    union all
    (select guest_team,
    case when guest_goals > host_goals then 3
        when guest_goals = host_goals then 1
        else 0 end as points
    from Matches)) 
    as tmp
on Teams.team_id = tmp.host_team
group by Teams.team_id
order by num_points desc,team_id

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