Question

I have data polling every x hours and it is based on a liquid level. The level always rises.

I need to know how to work out the average increase over a week (per day).

So if days data reads 1000-1200-1300-1400 then we know the average increase is 100 per day.

DateReceived  DeviceLevel Serial

1/mm/yyyy     3200         346
1/mm/yyyy     12000        222
2/mm/yyyy     3560         346
2/mm/yyyy     13600         222

Trying to use the

AVG()

function but to no evail.

Answer 1

You could use a self-join to find the level of the previous day. That gives you the increase for a day. An outer query could be used to find the average increase over a week:

select  datepart(wk, Day) as WeekNr
,       avg(IncreasePerDay) as AverageDailyIncrease
from    (
        select  cast(d1.MeasureDt as date) as Day
        ,       avg(d2.level) - avg(d1.level) as IncreasePerDay
        from    YourTable d1
        join    YourTable d2
        on      cast(d2.MeasureDt as date) = cast(d1.MeasureDt as date) + 1
        group by
                cast(d1.MeasureDt as date)
        ) as SubQueryAlias
group by
        datepart(wk, Day)