Datetime values generation MS SQL - sql

Question

There are two variables of the DateTime values available: for example, #STARTDATETIME = '2020-10-21 14:45' and #ENDDATETIME = '2020-10-22 19:00'
If there is only a single day between dates like STARTDATETIME = '2020-10-21 12:00' and ENDDATETIME = '2020-10-21 16:00' then the variables must save the initial values.
If there are one or more days between the values then the first date must start with the given timestamp to 16:00. The all in-between days time must be as from 08:00 till 16:00. And the last day must start with 08:00 time till the given timestamp.
Full example:
#STARTDATETIME = '2020-10-21 14:45' and #ENDDATETIME = '2020-10-23 19:15'
Desired output (table):
STARTDATETIME | ENDDATETIME
'2020-10-21 14:45' | '2020-10-21 16:00'
'2020-10-22 08:00' | '2020-10-22 16:00'
'2020-10-23 08:00' | '2020-10-23 19:15'

Answer 1

You can use a recursive CTE:
with dates as (
select #STARTDATETIME as startdt,
(case when datediff(day, #STARTDATETIME, #ENDDATETIME) = 0
then #ENDDATETIME
else dateadd(day, 1, convert(date, #STARTDATETIME))
end) as enddt
union all
select enddte,
(case when datediff(day, enddte, #ENDDATETIME) = 0
then #ENDDATETIME
else dateadd(day, 1, convert(date, enddte))
end) as enddt,
#ENDDATETIME as enddatetime
from dates
where enddt < #enddatetime
)
select *
from date;

Answer 2

This one will give you one row per day:
DECLARE #start dateTime = '20201021 14:45:00'
DECLARE #end dateTime = '20201023 19:15:00'
DECLARE #startDate Date = CAST(#start as date)
DECLARE #endDate Date = CAST(#end as date)
DECLARE #startTime Time = CAST(#start as time)
DECLARE #endTime Time = CAST(#end as time)
DECLARE #startOfDay DateTime = '08:00:00'
DECLARE #endOfDay DateTime = '16:00:00';
WITH lv0 AS (SELECT 0 g UNION ALL SELECT 0)
,lv1 AS (SELECT 0 g FROM lv0 a CROSS JOIN lv0 b) -- 4
,lv2 AS (SELECT 0 g FROM lv1 a CROSS JOIN lv1 b) -- 16
,lv3 AS (SELECT 0 g FROM lv2 a CROSS JOIN lv2 b) -- 256
,lv4 AS (SELECT 0 g FROM lv3 a CROSS JOIN lv3 b) -- 65,536
,lv5 AS (SELECT 0 g FROM lv4 a CROSS JOIN lv4 b) -- 4,294,967,296
,Tally (n) AS (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM lv5)
,
dates AS
(
SELECT
DateAdd(day,n-1,#startDate) as [Day]
FROM tally
WHERE n<=DATEDIFF(day,#startDate,#endDate)+1
)
select
[Day],
CASE WHEN [Day]=#startDate THEN #start ELSE CAST([DAY] AS DateTime)+#startOfDay END as [startOfWork],
CASE WHEN [Day]=#endDate THEN #end ELSE CAST([DAY] AS DateTime)+#endOfDay END as [endOfWork]
FROM dates
result:
| Day | startOfWork | endOfWork |
|------------|-------------------------|-------------------------|
| 2020-10-21 | 2020-10-21 14:45:00.000 | 2020-10-21 16:00:00.000 |
| 2020-10-22 | 2020-10-22 08:00:00.000 | 2020-10-22 16:00:00.000 |
| 2020-10-23 | 2020-10-23 08:00:00.000 | 2020-10-23 19:15:00.000 |