Can I perform the same functionality as this loop in sql? - coldfusion

Question

What I'm doing is checking for a gap between several dates, and calling the result a duplicate if there is not a 14 day gap from the last non-duplicate result.
The code looks like this in coldfusion:
<cfset date_check = data.date_to_check />
<cfset counted = 1 />
<cfloop query="data" >
#dateformat( date_to_check )# <br>
<cfif abs( dateDiff('d', date_check , data.date_to_check ) ) gt 14 >
<cfset counted ++ />
<cfset date_check = data.date_to_check />
Not Duplicate
<cfelseif currentrow gt 1>
Duplicate
<cfelse>
Not Duplicate
</cfif>
</cfloop>
> #counted#
And the output, for example will be:
19-Jan-18 Not Duplicate
16-Jan-18 Duplicate
21-Oct-16 Not Duplicate
12-Oct-16 Duplicate
06-Oct-16 Not Duplicate
22-Sep-16 Duplicate
09-Aug-16 Not Duplicate
11-Jul-16 Not Duplicate
> 5
I tried using outer apply and joining the next row that is 14 days from the current row. But the problem with this approach is if I have a cluster, it "resets" the date each row, like this:
19-Jan-18 - not duplicate
16-Jan-18 - duplicate
10-Jan-18 - will give false duplicate ( compares itself to Jan 16 instead of Jan 19 )
The query for this is something like this:
SELECT
count(*)
FROM #item T1
OUTER APPLY (
SELECT TOP 1 *
FROM #item T2
WHERE T2.[index] < T1.[index]
ORDER BY T2.[index] DESC) T
WHERE DATEDIFF(DAY, T.[date], T1.[date]) > 14

Answer 1

I think an EXISTS subquery would be the most straightforward way to do it. If that isn't performant enough, then you could do a join for it, but I find that EXISTS is generally fast enough and much easier to read.
SELECT ID,
Name,
Date_To_Check,
CASE
WHEN EXISTS (
SELECT 1
FROM Table1 b
WHERE b.Date_To_Check < a.Date_To_Check
AND DATEDIFF(d,b.Date_To_Check,a.Date_To_Check) <= 14
)
THEN 1
ELSE 0
END AS isDuplicate
FROM Table1 AS a