SQL difference in counter between two dates - sql

Question

I have a table like the below:
ID, MachineID Customer TimeStamp Counter type
1 A ABC 2017-10-25 3:08PM 1952 1
2 A ABC 2017-10-25 3:00PM 1940 1
3 A ABC 2017-10-25 12:05PM 1920 1
4 A ABC 2017-10-25 9:00AM 1900 1
5 B BCD 2017-10-25 3:11PM 1452 1
6 B BCD 2017-10-25 3:10PM 1440 1
7 B BCD 2017-10-25 12:15PM 1420 1
8 B BCD 2017-10-25 9:30AM 1400 1
9 A ABC 2017-10-23 3:08PM 1900 1
10 A ABC 2017-10-23 3:00PM 1840 1
11 A ABC 2017-10-23 12:05PM 1820 1
12 A ABC 2017-10-23 9:00AM 1800 1
13 B BCD 2017-10-23 3:11PM 1399 1
14 B BCD 2017-10-23 3:10PM 1340 1
15 B BCD 2017-10-23 12:15PM 1320 1
16 B BCD 2017-10-23 9:30AM 1300 1
The counter value increases whenever there is a click. I am trying to calculate number of clicks for each day by taking maximum counter value at the end of day and subtract the previous day maximum counter value and so on.
How do I do this in SQL server. Have to repeat this for each customer and Machine

Answer 1

Try this. I am using LAG function in order to achieve this. You can use where clause to filter out specific date you want :
Create table #counter(ID int, timeStamp datetime, Counter int, type int)
insert into #counter values
(1, '20171024 3:08PM' ,1952, 1),
(1, '20171025 3:00PM' ,1964, 1)
Select iq.*, (iq."counter" - iq.yesterday_counter) as today_count
from
(select id,
cast("timestamp" as date) as today_date,
"counter",
LAG("counter") over (order by cast("timestamp" as date)) yesterday_counter
from #counter
) iq
output:
id today_date counter yesterday_counter today_count
----------- ---------- ----------- ----------------- -----------
1 2017-10-24 1952 NULL NULL
1 2017-10-25 1964 1952 12

Answer 2

A SQL query to get the max counter for each day is:
SELECT CAST(timeStamp as date) AS [dateval]
,MAX(Counter) AS [maxCounter]
FROM YOURDATASET
GROUP BY CAST(timeStamp as date)
This is converting the datetime to date- cutting out the time, then taking the max(Counter).
One method to get the difference is to save the result in a temp datastructure, then query it to get the difference.
The question is whether your previous date is exactly the previous day, or if you're skipping days between counts, or taking the weekend off, etc. In that case you have to select the greatest previous date to the date being examined.
ex.
DECLARE #temp TABLE (dateval date, maxCounter int)
INSERT INTO #temp(dateval, maxCounter)
SELECT CAST(timeStamp as date) AS [dateval]
,MAX(Counter)
FROM YOURDATASET
GROUP BY CAST(timeStamp as date)
SELECT T.dateval
,T.dateval
-
(SELECT maxCounter
FROM #temp T2
WHERE T2.dateVal = (SELECT MAX(dateVal)
FROM #temp T3
WHERE T3.dateVal < T1.dateVal
)
) AS [Difference]
FROM #temp T
ORDER BY T.dateval