(select id from owner where date_format(auction_date,'%Y-%m-%d %H:%i:00') = date_format(NOW(),'%Y-%m-%d %H:%i:00')) as a
left join (select owner_id,max(nb) as maxbid from auction group by owner_id) as b on a.id=b.owner_id
left join (select owner_id,max(mb) as maxautobid from auction group by owner_id) as c on a.id=c.owner_id
For the second left join statement, i'm able to get the highest mb value. Can someone help me add a third left join statement so that i can get the second highest mb value??
对于第二个左连接语句,我可以获得最大的mb值。有人能帮我添加第三个左连接语句,以便我能得到第二个最大的mb值吗?
1 个解决方案
#1
3
First, you don't need a third join at all. You can do your calculation in one join:
首先,你根本不需要第三个连接。您可以在一个连接中进行计算:
from (select id
from owner
where date_format(auction_date,'%Y-%m-%d %H:%i:00') = date_format(NOW(),'%Y-%m-%d %H:%i:00')
) as a left join
(select owner_id, max(nb) as maxbid, max(mb) as maxautobi
from auction
group by owner_id
) b
on a.id=b.owner_id;
Getting the second largest value for mb
then uses a trick, involving substring_index()
and group_concat()
:
然后使用一个技巧获取mb的第二大值,包括substring_index()和group_concat():
from (select id
from owner
where date_format(auction_date,'%Y-%m-%d %H:%i:00') = date_format(NOW(),'%Y-%m-%d %H:%i:00')
) as a left join
(select owner_id, max(nb) as maxbid, max(mb) as maxautobi,
substring_index(substring_index(group_concat(mb order by mb desc), ',', 2), ',', -1
) as second_mb
from auction
group by owner_id
) b
on a.id=b.owner_id;
The idea is to concatenate the values together, ordering by mb
. Then take the second element of the list. The one downside is that the value is converted to a character string, even when it starts as a number.
其思想是将这些值连接在一起,按mb排序。然后取列表的第二个元素。一个缺点是该值被转换为字符串,即使它以数字开头。
#1
3
First, you don't need a third join at all. You can do your calculation in one join:
首先,你根本不需要第三个连接。您可以在一个连接中进行计算:
from (select id
from owner
where date_format(auction_date,'%Y-%m-%d %H:%i:00') = date_format(NOW(),'%Y-%m-%d %H:%i:00')
) as a left join
(select owner_id, max(nb) as maxbid, max(mb) as maxautobi
from auction
group by owner_id
) b
on a.id=b.owner_id;
Getting the second largest value for mb
then uses a trick, involving substring_index()
and group_concat()
:
然后使用一个技巧获取mb的第二大值,包括substring_index()和group_concat():
from (select id
from owner
where date_format(auction_date,'%Y-%m-%d %H:%i:00') = date_format(NOW(),'%Y-%m-%d %H:%i:00')
) as a left join
(select owner_id, max(nb) as maxbid, max(mb) as maxautobi,
substring_index(substring_index(group_concat(mb order by mb desc), ',', 2), ',', -1
) as second_mb
from auction
group by owner_id
) b
on a.id=b.owner_id;
The idea is to concatenate the values together, ordering by mb
. Then take the second element of the list. The one downside is that the value is converted to a character string, even when it starts as a number.
其思想是将这些值连接在一起,按mb排序。然后取列表的第二个元素。一个缺点是该值被转换为字符串,即使它以数字开头。