Calculate MonthlyVolume - PIVOT SQL - sql

Question

I am using SQL server 2008 and I have following Table with millions of rows...Here are few sample records
Serial_Num ReadingDate M_Counter Dyn_Counter
XYZ 3/15/2014 100 190
XYZ 4/18/2014 140 240
XYZ 5/18/2014 200 380
ABC 3/12/2014 45 40
ABC 4/19/2014 120 110
ABC 5/21/2014 130 155
This table will always have only one reading for each month and no missing months....
and I would like calculate M_Counter and Dyn_Counter values for each month, For an example XYZ -> May month calculated counter value should be 60 = 200 (05/18/2014 value) - 140 (04/18/2014 value). I would like to insert data into another table in following way.
CalculatedYear CalculatedMonth Serial_Num M_Counter_Calc Dyn_Counter_Calc
2014 4 XYZ 40 50
2014 5 XYZ 60 140
2014 4 ABC 75 70
2014 5 ABC 10 45
Any help really appreciated!

Answer 1

If you're using MS SQL, something like this should work. The concept is to sort the dataset based on Serial_Num and ReadingDate. Add a sequential Row ID and store into a temp table. Join the table onto itself such that you match up the current row with the previous row where the serial numbers still match. If there wasn't a prior month's reading, the value will be null. We use Isnull( x, 0) to account for this when doing the calculations.
declare #Temp1 table
(
RowID int,
Serial_Num varchar(3),
ReadingDate datetime,
M_Counter int,
Dyn_Counter int
)
insert into #Temp1
select ROW_NUMBER() over (order by Serial_Num, ReadingDate), *
from MyTable T
select
Year(T1.ReadingDate) As CalculatedYear,
Month(T1.ReadingDate) as CalculatedMonth,
T1.Serial_Num,
T1.M_Counter - ISNULL(T2.M_Counter,0) as Calculated_M_Counter,
T1.Dyn_Counter - isnull(T2.Dyn_Counter,0) as Calculated_Dyn_Counter
from #Temp1 T1
left outer join #Temp1 T2 on T1.RowID = T2.RowID + 1 and T1.Serial_Num = T2.Serial_Num
order by T1.Serial_Num, Year(T1.ReadingDate), Month(T1.ReadingDate)