How to Write Case Statement Using sys.time_zone_info - sql

Question

Need help in writing a Case statement to get the 'US Eastern Standard Time' from the sys.time_zone_info system view in SQL Server. There is an error in the Select statement and cannot figure out where. The CN.CreateDate is currently in UTC time and need to convert to EST taking into account Daylight Savings time.
select
CN.CreateDate
,case when (SELECT * FROM sys.time_zone_info TZI WHERE
TZI.name = 'US Eastern Standard Time'
AND ISNULL(TZI.is_currently_dst,0)=0)
THEN DATEADD(hour, -5,CN.CreateDate)
ELSE DATEADD(hour, -4,CN.CreateDate)
END AS CreateDateEST
from MC_CDCPContactNotes CN

Answer 1

This functionality is built into SQL Server with AT TIME ZONE, there's no need to re-invent the wheel here. Only thing to note is that you may need to convert to UTC then to your required zone first, e.g.
WITH MC_CDCPContactNotes AS
( SELECT t.CreateDate
FROM (VALUES (('20221225 00:00'), ('20220625 00:00')) AS t (CreateDate)
)
SELECT CN.CreateDate,
EasternTime = cn.CreateDate AT TIME ZONE 'UTC' AT TIME ZONE 'US Eastern Standard Time'
FROM MC_CDCPContactNotes CN;
Which gives:
CreateDate
EasternTime
2022-12-25
2022-12-24 19:00:00 -05:00
2022-06-25
2022-06-24 20:00:00 -04:00
Example on db<>fiddle

Answer 2

Just to fix your query:
select
CN.CreateDate
,case when (SELECT
count(*)
FROM sys.time_zone_info TZI
WHERE TZI.name = 'US Eastern Standard Time'
AND ISNULL(TZI.is_currently_dst,0)=0) = 1
THEN DATEADD(hour, -5,CN.CreateDate)
ELSE DATEADD(hour, -4,CN.CreateDate)
END AS CreateDateEST
from MC_CDCPContactNotes CN
But I would rewrite it like:
select
CN.CreateDate
,dateadd(hour,-5+ISNULL(TZI.is_currently_dst,0),CN.CreateDate) as CreateDateEst
from MC_CDCPContactNotes CN
join sys.time_zone_info TZI
on TZI.name = 'US Eastern Standard Time'