连接临时表

SELECT DAY(temp.last14day), ifnull(sum(orders.price), 0) as 'total'
FROM (      
            select curdate() - INTERVAL (last14.num14) DAY as last14day     from (  select  0   as  num14   
            union all select 1             union all select 2             union all select 3             union all select 4             union all select 5             
            union all select 6             union all select 7             union all select 8             union all select 9             union all select 10
            union all select 11            union all select 12            union all select 13            union all select 14            ) as last14
) as temp
left join orders on date_format(orders.created_at, '%Y-%m-%d') = temp.last14day group by temp.last14day order by temp.last14day desc limit 15;