SQL Server 2012 - Select queries leap year - sql-server

Question

I have a little issue with one my queries. The entire query is actually is a little long since it includes a UNION ALL.
SELECT 'ITV' = CASE WHEN tblIntake.StaffID Is Null THEN '<Unknown>' ELSE
(tblStaffMember.StaffLast + ', ' + tblStaffMember.StaffFirst + CASE WHEN
tblStaffMember.StaffMI Is Null THEN '' ELSE ' ' + tblStaffMember.StaffMI END) END,
tblMember.[LAST], tblMember.[FIRST],
'DueDate' = DATEADD(m, 6,CAST(CONVERT(Varchar(10),
MONTH(tblIntake.EnrollDate)) + '/' + CONVERT(Varchar(10),
DAY(tblIntake.EnrollDate)) + '/' + CONVERT(Varchar(10),YEAR(GETDATE()))As
DateTime)), 'Type' = '6 Month Appt'
From tblIntake LEFT JOIN tblStaffMember ON tblIntake.StaffID =
tblStaffMember.StaffID LEFT JOIN tblMember ON
tblIntake.KEY = tblMember.KEY
Where tblIntake.UnEnrollDate Is Null AND
DATEADD(m,6,CAST(CONVERT(Varchar(10),MONTH(tblIntake.EnrollDate)) + '/' +
CONVERT(Varchar(10),DAY(tblIntake.EnrollDate)) + '/' +
CONVERT(Varchar(10),YEAR(GETDATE()))As DateTime)) > GETDATE() AND
DATEADD(m, 6,CAST(CONVERT(Varchar(10),MONTH(tblIntake.EnrollDate)) + '/' +
CONVERT(Varchar(10),DAY(tblIntake.EnrollDate)) + '/' +
CONVERT(Varchar(10),YEAR(GETDATE()))As DateTime)) <= DATEADD(d, 45, GETDATE())
So, I have this wonderful query. Everything was running okay until a user entered a leap year date for ENROLLDATE in tblIntake. How would I go about fixing it? My other UNION does the same SELECT statements with the exception of for when it does
CONVERT(VARCHAR(10),YEAR(GetDate()-1)) as DateTime > '4th line from the bottom
CONVERT(VARCHAR(10),YEAR(GetDate()-1)) as DateTime > '2nd line from the bottom
EDIT:
Receiving this error when I run the query
Msg 242, Level 16, State 3, Line 1
The conversion of a varchar data type to a datetime data type resulted in an out-of-range value.
I tried running the separate queries, and it seems like I'm only getting the error when I do this..
CONVERT(VARCHAR(10),YEAR(GetDate()-1)) as DateTime > '4th line from the bottom
CONVERT(VARCHAR(10),YEAR(GetDate()-1)) as DateTime > '2nd line from the bottom
After UNION ALL
EDIT 2:
I've been working off Sean's answer which makes more sense. Here is the code that I've got....
SELECT 'CSC' = case when tblIntake.staffID is null Then '<notIndicated>' Else (tblStaffMember.staffLast + ',' + tblStaffMember.StaffFirst + case when tblStaffMember.staffMI is null then '' else ' ' + tblStaffMember.staffMI END)end
, tblMember.[Last], tblMember.[First]
,'Due' = DateADD(m,6,cast(tblIntake.enrolldate as datetime))
,'Type' = '6 Month Review'
from tblMembEnrollment
left join tblStaffMember on tblIntake.staffID = tblStaffMember.staffID
left join tblMember on tblIntake.SBkey=tblMember.sbkey
where tblIntake.unEnrollDate is null and dateAdd(m, 6, tblIntake.enrolldate) > GETDATE()
and dateadd(m, 6, cast(tblIntake.enrolldate as DateTime))<= DateAdd(d,45,GetDate())
The issue I'm seeing is that in the old query, when the code takes apart the EnrollDate into days, months and years for years it used GET DATE, see below in between *** ****
Where tblIntake.UnEnrollDate Is Null AND
DATEADD(m,6,CAST(CONVERT(Varchar(10),MONTH(tblIntake.EnrollDate)) + '/' +
CONVERT(Varchar(10),DAY(tblIntake.EnrollDate)) + '/' +
CONVERT(Varchar(10),***YEAR(GETDATE()))As DateTime))*** > GETDATE()
Now it was easier done this way since he did take it apart, how is it that I can do it with my full Enroll date.

Answer 1

If I understand what you are trying to do here you can greatly simplify this. Please note that I used aliases everywhere instead of repeating the table name over and over. Also, I used the datepart names instead of the abbreviations as they are much more clear. Last but not least I just used the existing datetime value. I converted them to the date datatype as what it appears the existing logic is doing is converting it to a date value to avoid the time portion. This as fairly common prior to 2005 when the date datatype was added. I also reduced all the nested case expressions into something much easier to read.
SELECT 'ITV' = ISNULL(sm.StaffLast + ', ' + sm.StaffFirst + ISNULL(' ' + sm.StaffMI, ''), '<Unknown>')
, tblMember.[LAST]
, tblMember.[FIRST]
, 'DueDate' = DATEADD(month, 6, convert(date, tblIntake.EnrollDate))
, 'Type' = '6 Month Appt'
From tblIntake i
LEFT JOIN tblStaffMember sm ON i.StaffID = sm.StaffID
LEFT JOIN tblMember m ON i.KEY = m.KEY
Where i.UnEnrollDate Is Null
AND DATEADD(month, 6, convert(date, i.EnrollDate)) > GETDATE()
AND DATEADD(month, 6, convert(date, i.EnrollDate)) <= DATEADD(day, 45, GETDATE())
--EDIT--
With the clarity of rules I think this should be what you are looking for. This has the advantage of also being SARGable so that any index on i.EnrollDate can be utilized.
Where i.UnEnrollDate Is Null
AND convert(date, i.EnrollDate) > DATEADD(month, -6, GETDATE())
AND convert(date, i.EnrollDate) <= DATEADD(day, -45, GETDATE())

Answer 2

I'd replace all of those date parts and converts with dateadd, something like:
declare #test datetime
set #test = '2-29-2016'
select cast(#test as varchar(11))
, cast(dateadd(mm, 6, #test) as varchar(11))
, cast(dateadd(yy, -1, #test) as varchar(11))
If you keep the dates as datetimes, SQL server will automatically correct for leap years, shorter months, etc. The query above returns:
Feb 29 2016 Aug 29 2016 Feb 28 2015