MySQL获取选定行的最大值和最小值之间的差异

Question

我想要一个查询，获取按天分组的最大值和最小值之间的差异。我尝试不起作用：

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`); 

每个sub_meter有可能是> 3000的值，但只能通过< 10每天不同。我想要的差异，即结果< 10.通过上面的查询，我得到的结果> 3000。

下面的查询，只选择一个米，并给出正确的结果，最大值（17531），最小值（17523）和差值（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) 

但添加另一个米到条款，给出一个坏的结果，最大为17531，和最小是3021，该差异是14510.但我想每个流量计的差异，然后相加。

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) 

我已经试过另一种尝试：

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

查询只能由日（日）分组，但你要组也计，所以你需要添加到您的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，如果你要总结一天的不同，你可以这样做：

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，如果你想通过仪表来概括：

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