MySQL獲得選擇行的最大值和最小值之間的差異

Question

我想要一個查詢，該查詢獲取按天分組的最大值和最小值之間的差異。 我的嘗試不起作用：

SELECT date(`date`), 
   (max(value) - min(value)) as value,
FROM `sub_meter_data` 
where date(sub_meter_data.date) > '2012-10-01' 
  and sub_meterID in('58984','58985','58986','58987')
group by date(`date`);

每個sub_meter的值可能大於3000，但每天相差僅<10。 我想要差異，即結果<10。 通過上面的查詢，我得到的結果> 3000。

下面的查詢僅選擇一個儀表，並給出正確的結果，即最大值（17531），最小值（17523）和差（8）。

SELECT date(sub_meter_data.date) as date,
   max(value) as max_meter,
   min(value) as min_meter, 
   max(value) - min(value) as diff,
FROM `sub_meter_data`
where date(sub_meter_data.date) > '2012-10-01' 
  and sub_meterID in('57636')
  group by date(sub_meter_data.date)

但是在in子句中添加另一個儀表，會得出不好的結果，最大值是17531，最小值是3021，差異是14510。但是我想要每個儀表的差異，然后求和。

SELECT date(sub_meter_data.date) as date,
   max(value) as max_meter,
   min(value) as min_meter, 
   max(value) - min(value) as diff,
   FROM `sub_meter_data`
where date(sub_meter_data.date) > '2012-10-01' 
  and sub_meterID in('57636', '57628')
  group by date(sub_meter_data.date)

我嘗試過的另一種嘗試是：

SELECT date(sub_meter_data.date) as date,
   sum(CASE WHEN sub_meterID = '57628' OR sub_meterID = '57636' THEN (max(value) -     min(value)) ELSE 0 END) as value
   FROM `sub_meter_data`
where date(sub_meter_data.date) > '2012-10-01' 

Answer 1

該查詢僅按天（日期）分組，但您也想按米分組，因此需要按以下方式將其添加到group by ：

select sub_meterID, date(`date`) as day, max(value) - min(value) as value
from `sub_meter_data`
where date(`date`) > '2012-10-01'
    and sub_meterID in ('58984','58985','58986','58987')
group by sub_meterID, date(`date`);

然后，如果您想按天總結差異，則可以執行以下操作：

select day, sum(diff) as total_diff
from (
    select sub_meterID, date(`date`) as day, max(value) - min(value) as diff
    from `sub_meter_data`
    where date(`date`) > '2012-10-01'
       and sub_meterID in ('58984','58985','58986','58987')
    group by sub_meterID, date(`date`)
    ) a
group by day

或者，如果您想按米求和：

select sub_meterID, sum(diff) as total_diff
from (
    select sub_meterID, date(`date`) as day, max(value) - min(value) as diff
    from `sub_meter_data`
    where date(`date`) > '2012-10-01'
       and sub_meterID in ('58984','58985','58986','58987')
    group by sub_meterID, date(`date`)
    ) a
group by sub_meterID