Question

这里的另一个小问题。我必须合并两个不同的表。在第一个中，我必须找到一小时日期时间范围内的平均外部温度。换句话说，我必须在一小时的日期时间范围内计算每小时千瓦的使用量。单个查询完美地运行，但是当我尝试加入它们时，它们不起作用。此查询不起作用：

select dataora, AVG(Test) 
from temperature 
where dataora between '2013-11-01' and '2013-11-31' GROUP BY date(dataora),hour(dataora)
natural join (
    SELECT
      (t1.dt) AS time,(case
     when t1.value>t2.value AND t2.value>0
          then abs(t1.value - t2.value)
     when t1.value>t2.value AND t2.value=0
          then t2.value
          else t1.value END)kwhg, 
     (case
     when t1.value1>t2.value1 AND t2.value1>0
          then abs(t1.value1 - t2.value1)
     when t1.value1>t2.value1 AND t2.value1=0
          then t2.value1
     when t1.value1=t2.value1 AND t1.value1>0 
        then abs(t1.value1 - t2.value1)
      else 0 END) kwhc, 
      (case
     when t1.value2>t2.value2 AND t2.value2>0
          then abs(t1.value2 - t2.value2)
     when t1.value2>t2.value2 AND t2.value2=0
          then t2.value2
     when t1.value2=t2.value2 AND t1.value2>0 
        then abs(t1.value2 - t2.value2)
      else 0 END)kwhi,
    (case
     when t1.value3>t2.value3 AND t2.value3>0
          then abs(t1.value3 - t2.value3)
     when t1.value3>t2.value3 AND t2.value3=0
          then t2.value3
     when t1.value3=t2.value3 AND t1.value3>0 
        then abs(t1.value3 - t2.value3)
      else 0 END) kwhfm
    FROM 
        (SELECT (dataora) dt, MAX(kwhg) value, MAX(kwhc) value1, MAX(kwhi) value2, MAX(kwhfm) value3  FROM misure where dataora between '2013-11-01' and '2013-11-31' GROUP BY date(dt),hour(dt)) t1
        JOIN
        (SELECT (dataora) dt, MAX(kwhg) value, MAX(kwhc) value1, MAX(kwhi) value2, MAX(kwhfm) value3  FROM misure where dataora between '2013-11-01' and '2013-11-31' GROUP BY date(dt),hour(dt)) t2
        on t1.dt = t2.dt + interval 1 hour) t3

这个只给我一行（第一行，而不是本例中需要的720行）：

    SELECT
      (t1.dt) AS time,(case
     when t1.value>t2.value AND t2.value>0
          then abs(t1.value - t2.value)
     when t1.value>t2.value AND t2.value=0
          then t2.value
          else t1.value END)kwhg, 
     (case
     when t1.value1>t2.value1 AND t2.value1>0
          then abs(t1.value1 - t2.value1)
     when t1.value1>t2.value1 AND t2.value1=0
          then t2.value1
     when t1.value1=t2.value1 AND t1.value1>0 
        then abs(t1.value1 - t2.value1)
      else 0 END) kwhc, 
      (case
     when t1.value2>t2.value2 AND t2.value2>0
          then abs(t1.value2 - t2.value2)
     when t1.value2>t2.value2 AND t2.value2=0
          then t2.value2
     when t1.value2=t2.value2 AND t1.value2>0 
        then abs(t1.value2 - t2.value2)
      else 0 END)kwhi,
    (case
     when t1.value3>t2.value3 AND t2.value3>0
          then abs(t1.value3 - t2.value3)
     when t1.value3>t2.value3 AND t2.value3=0
          then t2.value3
     when t1.value3=t2.value3 AND t1.value3>0 
        then abs(t1.value3 - t2.value3)
      else 0 END) kwhfm, AVG(Test)
    FROM 
        (SELECT (dataora) dt, MAX(kwhg) value, MAX(kwhc) value1, MAX(kwhi) value2, MAX(kwhfm) value3  FROM misure where dataora between '2013-11-01' and '2013-11-31' GROUP BY date(dt),hour(dt)) t1
        JOIN
        (SELECT (dataora) dt, MAX(kwhg) value, MAX(kwhc) value1, MAX(kwhi) value2, MAX(kwhfm) value3  FROM misure where dataora between '2013-11-01' and '2013-11-31' GROUP BY date(dt),hour(dt)) t2
        on t1.dt = t2.dt + interval 1 hour
natural join temperature

我使用自然连接，因为我需要每小时真正的千瓦和每小时外部温度的4个测量值（每15分钟）的平均值。也许答案很简单，但我还没有找到它！在此先感谢您的任何帮助

Answer 1

请勿使用natural join。它连接在具有相同名称的所有字段上。相反，做一个正常的连接（我猜是inner join或left outer join）并在日期使用on子句：

(<subquery 1>) s1 join
(<subquery 2>) s2
on s1.time = s2.time

通过查询自然加入两组之间

1 个答案: