How to get data by datetime logic in sql - sql-server

Question

I have date(dt col name) column in est.
If i execute query between '7:30pm'EST and '11:59' Est timezone.i should get previous day information and if i execute after 12:00 i need to get today's information.
I have tried this:
Case when getdate() between '2021-03-09 7:30:00' and '2021-03-09 11:59:00'
Then dt=getdate() -1
else dt=getdate()

Answer 1

If I understand your question correctly, then you want to retrieve different rows depending on the time when the query is executed.
Using a case expression can work, but then you have to move the comparison with the case expression result outside the case expression.
So instead of:
... where case when <condition> then (Column = Value1) else (Column = Value2) end
do this:
... where Column = (case when <condition> then Value1 else Value2 end)
where the parentheses are added here for clarity.
Sample data
create table MyTable
(
dt date,
data nvarchar(20)
);
insert into MyTable (dt, data) values
('2021-03-08', 'yesterday''s data'),
('2021-03-09', 'today''s data');
Solution
Applying the construction from the start of my answer. Unit testing both options of the case expression will require a separate variable (or you could just wait hours and hours...).
Requesting data on today's date in period [07:30, 11:59]
declare #referenceDate smalldatetime = '2021-03-09 10:20';
--> using date variable instead of 'getdate()' for demo purposes !
select mt.dt,
mt.data
from MyTable mt
where mt.dt = case
when #referenceDate between '2021-03-09 07:30:00' and '2021-03-09 11:59:00'
then dateadd(day, -1, convert(date, #referenceDate))
else convert(date, #referenceDate)
end;
--> returns data from yesterday
Requesting data on today's date outside period [07:30, 11:59]
declare #referenceDate smalldatetime = '2021-03-09 17:40';
--> using date variable instead of 'getdate()' for demo purposes !
select mt.dt,
mt.data
from MyTable mt
where mt.dt = case
when #referenceDate between '2021-03-09 07:30:00' and '2021-03-09 11:59:00'
then dateadd(day, -1, convert(date, #referenceDate))
else convert(date, #referenceDate)
end;
--> returns data from today
Requesting data on any date depending on period [07:30, 12:00]
select mt.dt,
mt.data
from MyTable mt
where mt.dt = case
when convert(time, getdate()) >= '07:30:00'
and convert(time, getdate()) < '12:00:00'
then dateadd(day, -1, convert(date, getdate()))
else convert(date, getdate())
end;
--> returns data from today OR yesterday depeding on time of execution (in/outside [07:30, 12:00])
Your question also mentions the EST timezone. If you want the current execution time to be interpreted as EST, then have a look a this question and this documentation page. Whether you should store data in EST instead of UTC in the first place is a whole other question... You will end up with something like this.
-- converting the query reference time to EST
declare #referenceDate smalldatetime = (select getdate() at time zone 'Eastern Standard Time');
select mt.dt,
mt.data
from MyTable mt
where mt.dt = case
when convert(time, #referenceDate) >= '07:30:00'
and convert(time, #referenceDate) < '12:00:00'
then dateadd(day, -1, convert(date, #referenceDate))
else convert(date, #referenceDate)
end;
Fiddle to see everything in action.