Question

我有这个查询。返回每日的最低和最高温度：

def max_date_prior_to_year(dates, yr):
     return dates[dates<pd.to_datetime(str(yr)+'-01-01')].max()

我在此查询中缺少两个字段LowTime和MaxTime。我不知道如何获得最小（低）和最大（高）发生的时间。（DateTimeS是一个DateTime字段，其余为十进制）该表具有逐分钟的温度数据，如下所示：

select  year(DateTimeS),month(DateTimeS),day(DateTimeS),min(Low),max(High) from temperature
where year(DateTimeS) = 2018
group by year(DateTimeS),month(DateTimeS),day(DateTimeS)

有什么想法吗？

Answer 1

在MariaDB 10.3中，您应该能够使用窗口功能。所以：

select year(DateTimeS), month(DateTimeS), day(DateTimeS),
       min(Low), max(High),
       max(case when seqnum_l = 1 then DateTimeS end) as dateTimeS_at_low,
       max(case when seqnum_h = 1 then DateTimeS end) as dateTimeS_at_high
from (select t.*,
             row_number() over (partition by date(DateTimeS) order by low) as seqnum_l,
             row_number() over (partition by date(DateTimeS) order by high desc) as seqnum_h
      from temperature t
     ) t
where year(DateTimeS) = 2018
group by year(DateTimeS), month(DateTimeS), day(DateTimeS);

MariaDB / MySQL。查找分组中具有最大值和最小值的行字段

1 个答案: