SQL Query to return 24 hour, hourly count even when no values exist?

Question

I\'ve written a query that groups the number of rows per hour, based on a given date range.

SELECT CONVERT(VARCHAR(8),TransactionTime,101) + \' \' + CONVERT(         


        

Answer 1

You do this by building first the 23 hours table, the doing an outer join against the transactions table. I use, for same purposes, a table valued function:

create function tvfGetDay24Hours(@date datetime)
returns table
as return (
select dateadd(hour, number, cast(floor(cast(@date as float)) as datetime)) as StartHour
  , dateadd(hour, number+1, cast(floor(cast(@date as float)) as datetime)) as EndHour
from master.dbo.spt_values
where number < 24 and type = 'p');

Then I can use the TVF in queries that need to get 'per-hour' basis data, even for missing intervals in the data:

select h.StartHour, t.TotalHourlyTransactions
from tvfGetDay24Hours(@StartDate) as h
outer apply (
  SELECT 
    COUNT(TransactionID) AS TotalHourlyTransactions
    FROM MyTransactions 
    WHERE TransactionTime BETWEEN h.StartHour and h.EndHour
    AND TerminalId = @TerminalID) as t
order by h.StartHour

Updated

Example of a TVF that returns 24hours between any arbitrary dates:

create function tvfGetAnyDayHours(@dateFrom datetime, @dateTo datetime)
returns table
as return (
select dateadd(hour, number, cast(floor(cast(@dateFrom as float)) as datetime)) as StartHour
  , dateadd(hour, number+1, cast(floor(cast(@dateFrom as float)) as datetime)) as EndHour
from master.dbo.spt_values
where type = 'p'
and number < datediff(hour,@dateFrom, @dateTo) + 24);

Note that since master.dbo.spt_values contains only 2048 numbers, the function will not work between dates further apart than 2048 hours.