Difference Max and Min from Different Dates - sql

Question

I'm going to try to explain this the best I can.
The code below does the following:
Finds a service address from the ServiceLocation table.
Finds a service type (electric or water).
Finds how many days in the past to pull data.
Once it has this, it calculates the "daily usage" by subtracting the max meter read for a day from the minimum meter read for a day.
(MAX(mr.Reading) - MIN(mr.Reading)) AS 'DaytimeUsage'
However, what I'm missing is the max reading from the day prior and the minimum reading from the current day. Mathematically, this should look something like this:
MAX(PriorDayReading) - MIN(ReadDateReading)
Essentially, if it goes back 5 days it should kick out a table that reads as follows:
Service Location | Read Date | Usage |
123 Main St | 4/20/15 | 12 |
123 Main St | 4/19/15 | 8 |
123 Main St | 4/18/15 | 6 |
123 Main St | 4/17/15 | 10 |
123 Main St | 4/16/15 | 11 |
Where "Usage" is the 'DaytimeUsage' + usage that I'm missing (and the question above). For example, 4/18/15 would be the 'DaytimeUsage' in the query below PLUS the the difference between the MAX read from 4/17/15 and the MIN read from 4/18/15.
I'm not sure how to accomplish this or if it is possible.
SELECT
A.ServiceAddress AS 'Service Address',
convert(VARCHAR(10),A.ReadDate,101) AS 'Date',
SUM(A.[DaytimeUsage]) AS 'Usage'
FROM
(
SELECT
sl.location_addr AS 'ServiceAddress',
convert(VARCHAR(10),mr.read_date,101) AS 'ReadDate',
(MAX(mr.Reading) - MIN(mr.Reading)) AS 'DaytimeUsage'
FROM
DimServiceLocation AS sl
INNER JOIN FactBill AS fb ON fb.ServiceLocationKey = sl.ServiceLocationKey
INNER JOIN FactMeterRead as mr ON mr.ServiceLocationKey = sl.ServiceLocationKey
INNER JOIN DimCustomer AS c ON c.CustomerKey = fb.CustomerKey
WHERE
c.class_name = 'Tenant'
AND sl.ServiceLocationKey = #ServiceLocation
AND mr.meter_type = #ServiceType
GROUP BY
sl.location_addr,
convert(VARCHAR(10),
mr.read_date,101)
) A
WHERE A.ReadDate >= GETDATE()-#Days
GROUP BY A.ServiceAddress, convert(VARCHAR(10),A.ReadDate,101)
ORDER BY convert(VARCHAR(10),A.ReadDate,101) DESC

Answer 1

It seems like you could solve this by just calculating the difference between the MAX of yesterday & today, however this is how I would approach it. Join to the same table again for the previous day relative to any given day, and select the Max/Min for that too within your inner query. Also if you place the date in the inner query where clause the data set you return will be quicker & smaller.
SELECT
A.ServiceAddress AS 'Service Address',
convert(VARCHAR(10),A.ReadDate,101) AS 'Date',
SUM(A.[TodayMax]) - SUM(A.[TodayMin]) AS 'Usage',
SUM(A.[TodayMax]) - SUM(A.[YesterdayMax]) AS 'Usage with extra bit you want'
FROM
(
SELECT
sl.location_addr AS 'ServiceAddress',
convert(VARCHAR(10),mr.read_date,101) AS 'ReadDate',
MAX(mrT.Reading) AS 'TodayMax',
MIN(mrT.Reading) AS 'TodayMin',
MAX(mrY.Reading) AS 'YesterdayMax',
MIN(mrY.Reading) AS 'YesterdayMin',
FROM
DimServiceLocation AS sl
INNER JOIN FactBill AS fb ON fb.ServiceLocationKey = sl.ServiceLocationKey
INNER JOIN FactMeterRead as mrT ON mrT.ServiceLocationKey = sl.ServiceLocationKey
INNER JOIN FactMeterRead as mrY ON mrY.ServiceLocationKey = s1.ServiceLocationKey
AND mrY.read_date = mrT.read_date -1)
INNER JOIN DimCustomer AS c ON c.CustomerKey = fb.CustomerKey
WHERE
c.class_name = 'Tenant'
AND sl.ServiceLocationKey = #ServiceLocation
AND mr.meter_type = #ServiceType
AND convert(VARCHAR(10), mrT.read_date,101) >= GETDATE()-#Days
GROUP BY
sl.location_addr,
convert(VARCHAR(10),
mr.read_date,101)
) A
GROUP BY A.ServiceAddress, convert(VARCHAR(10),A.ReadDate,101)
ORDER BY convert(VARCHAR(10),A.ReadDate,101) DESC

Answer 2

You can use the APPLY operator if you are above sql server 2005. Here is a link to the documentation. https://technet.microsoft.com/en-us/library/ms175156(v=sql.105).aspx The APPLY operation comes in two forms OUTER APPLY AND CROSS APPLY - OUTER works like a left join and CROSS works like an inner join. They let you run a query once for each row returned. I setup my own sample of what you were trying to do, here it is and I hope it helps.
http://sqlfiddle.com/#!6/fdb3f/1
CREATE TABLE SequencedValues (
Location varchar(50) NOT NULL,
CalendarDate datetime NOT NULL,
Reading int
)
INSERT INTO SequencedValues (
Location,
CalendarDate,
Reading
)
SELECT
'Address1',
'4/20/2015',
10
UNION SELECT
'Address1',
'4/19/2015',
9
UNION SELECT
'Address1',
'4/19/2015',
20
UNION SELECT
'Address1',
'4/19/2015',
25
UNION SELECT
'Address1',
'4/18/2015',
8
UNION SELECT
'Address1',
'4/17/2015',
7
UNION SELECT
'Address2',
'4/20/2015',
100
UNION SELECT
'Address2',
'4/20/2015',
111
UNION SELECT
'Address2',
'4/19/2015',
50
UNION SELECT
'Address2',
'4/19/2015',
65
SELECT DISTINCT
sv.Location,
sv.CalendarDate,
sv_dayof.MINDayOfReading,
sv_daybefore.MAXDayBeforeReading
FROM SequencedValues sv
OUTER APPLY (
SELECT MIN(sv_dayof_inside.Reading) AS MINDayOfReading
FROM SequencedValues sv_dayof_inside
WHERE sv.Location = sv_dayof_inside.Location
AND sv.CalendarDate = sv_dayof_inside.CalendarDate
) sv_dayof
OUTER APPLY (
SELECT MAX(sv_daybefore_max.Reading) AS MAXDayBeforeReading
FROM SequencedValues sv_daybefore_max
WHERE sv.Location = sv_daybefore_max.Location
AND sv_daybefore_max.CalendarDate IN (
SELECT TOP 1 sv_daybefore_inside.CalendarDate
FROM SequencedValues sv_daybefore_inside
WHERE sv.Location = sv_daybefore_inside.Location
AND sv.CalendarDate > sv_daybefore_inside.CalendarDate
ORDER BY sv_daybefore_inside.CalendarDate DESC
)
) sv_daybefore
ORDER BY
sv.Location,
sv.CalendarDate DESC

Answer 3

I'm not sure I full understood your db structure but I may have a solution so feel free to edit my answer to adapt or correct any mistake.
The idea is to use two aliases for the table FactMeterRead. mrY (Y as yesterday) and mrT (T as Today). And differentiate them with a read_date restriction.
However I didn't understand enough your tables to write a fully functional query. I hope you will get the idea anyway with this example.
SELECT
sl.location_addr AS 'ServiceAddress',
convert(VARCHAR(10),mrT.read_date,101) AS 'ReadDate',
(MAX(mrY.Reading) - MIN(mrT.Reading)) AS 'DaytimeUsage'
FROM
DimServiceLocation AS sl
INNER JOIN FactMeterRead as mrY ON mrY.ServiceLocationKey = sl.ServiceLocationKey
INNER JOIN FactMeterRead as mrT ON mrT.ServiceLocationKey = sl.ServiceLocationKey
WHERE mrY.read_date=DATE_SUB(mrT.read_date,1 DAY)