SQL Server counting hours between dates excluding Fri 6pm - Mon 6am

Question

I am looking for a SQL server function which can count the number of hours between 2 given datetime values, but excludes the hours between 6pm on Friday and 6am on Monday. <

Answer 1

This uses a number table. Adjust weekend start/end in parmeters:

declare @d1 as datetime = '2018-06-01 05:30:00'
    , @d2 as datetime = '2018-06-18 19:45:00'
    , @FridayWE as int = 18 --6pm
    , @MondayWS as int = 6  --6am

;WITH x AS (SELECT n FROM (VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) v(n))
select count(*) as HoursBetweenDatetimes
from (
    SELECT dateadd(hour, ones.n + 10*tens.n + 100*hundreds.n + 1000*thousands.n, dateadd(hour, datediff(hour, 0, @d1), 0)) as [DateHour]
    FROM x ones,     x tens,      x hundreds,       x thousands
    ) a
where not ((DATEPART(dw,[DateHour]) = 6 and DATEPART(hour,[DateHour]) >= @FridayWE)
or (DATEPART(dw,[DateHour]) = 7 )
or (DATEPART(dw,[DateHour]) = 1 )
or (DATEPART(dw,[DateHour]) = 2 and DATEPART(hour,[DateHour]) < @MondayWS))
and [DateHour] < @d2