While Loop SQL not populating complete results - sql

Question

Question: the iteration happens only till record 131 and gives accurate value, after that the parameter #ADE_END_DATE returns a NULL value, why would that be? Below is my code.
Additionally I noticed the column Leave_Date has NULL values and the iteration stops and returns NULL value for the parameter #ADE_END_DATE where the NULL value starts.
Thanks for your help.
BEGIN
DECLARE #HIREDATEPlus1Yr DATETIME
DECLARE #ADE_Leave_Date DATETIME
DECLARE #ADE_End_Date DATETIME
DECLARE #ADE_Start_Date DATETIME
DECLARE #DATECAL DATETIME
DECLARE #i INT
DECLARE #j INT
DECLARE #Loop_length INT
DECLARE #ID VARCHAR(18)
-- start of loop
SET #j = 1
-- Loop length will equal to the list of all ADRs
SET #Loop_Length = (SELECT COUNT([AD_ID])
FROM [DS_ADHOC_MOPs].[ADE].[List]
WHERE Status NOT IN ('MANAGER', 'TBH', 'FROZEN'))
-- Loop through each ADRs
WHILE (#j <= #Loop_length)
BEGIN
-- Loop through each ADRs
SET #i = 0
-- Find AD ID
SET #ID = (SELECT TOP 1 [AD_ID] FROM [DS_ADHOC_MOPs].[ADE].[List]
WHERE [AD_ID] NOT IN (SELECT TOP (#j-1) [AD_ID]
FROM [DS_ADHOC_MOPs].[ADE].[List]
WHERE ([AD_ID] IS NOT NULL
AND Status NOT IN ('MANAGER', 'TBH', 'FROZEN'))))
-- Find the start date of the ADR
SET #ADE_Start_Date = (SELECT TOP 1 [Hire_Date]
FROM [DS_ADHOC_MOPs].[ADE].[List]
WHERE [AD_ID] NOT IN (SELECT TOP (#j-1) [AD_ID]
FROM [DS_ADHOC_MOPs].[ADE].[List]
WHERE ([AD_ID] IS NOT NULL
AND Status NOT IN ('MANAGER', 'TBH', 'FROZEN'))))
-- Hire date plus 1 year
SET #HIREDATEPlus1Yr = DATEADD(YEAR, 1, #ADE_Start_Date)
--Adding Leave Date
SET #ADE_Leave_Date = (SELECT TOP 1 [LEAVE_DATE]
FROM [DS_ADHOC_MOPs].[ADE].[List]
WHERE [AD_ID] NOT IN (SELECT TOP (#j-1) [AD_ID]
FROM [DS_ADHOC_MOPs].[ADE].[List]
WHERE ([AD_ID] IS NOT NULL
AND Status NOT IN ('MANAGER', 'TBH', 'FROZEN'))))
-- Set a temporary variable which will be 1 year from now. Use the Date ADD formulae to start date, if they are leaver before one year then add leave date (Use IF): DONE
-- Put everything inside the while loop and add opportunity selecting to it.
IF #ADE_Leave_Date IS NULL
SET #ADE_End_Date = DATEADD(YEAR, 1, #ADE_Start_Date)
ELSE IF #HIREDATEPlus1Yr < #ADE_Leave_Date
SET #ADE_End_Date = DATEADD(YEAR, 1, #ADE_Start_Date)
ELSE
SET #ADE_End_Date = #ADE_Leave_Date
SET #DATECAL = datediff(DAY, #ADE_Start_Date, #ADE_End_Date)
SET #j = #j + 1
UPDATE #TEMPTABLEEEE
SET [#ADE_End_Date] = #ADE_End_Date
WHERE #ID = AD_ID
END
SELECT * FROM #TEMPTABLEEEE
END

Answer 1

I'm not sure why you are using a WHILE loop. It looks like this code could be much simplified. SQL is a set based language. Whenever possible, you should try to handle your data as a whole set instead of breaking it down into row by row evaluations.
Does this give you what you need? If the table has more than one row for each AD_ID, you will need to get the MAX() or MIN() Hire_Date/LEAVE_DATE. To improve the answer, consider providing sample data.
UPDATE t
SET [#ADE_End_Date] = ed.ADE_EndDate
FROM #TEMPTABLEEEE AS t
INNER JOIN (
SELECT AD_ID
,CASE
WHEN LEAVE_DATE IS NULL THEN DATEADD(YEAR,1,Hire_Date)
WHEN DATEADD(YEAR,1,Hire_Date) < LEAVE_DATE THEN DATEADD(YEAR,1,Hire_Date)
ELSE LEAVE_DATE
END AS ADE_EndDate
FROM DS_ADHOC_MOPs.ADE.List
WHERE Status NOT IN ('MANAGER', 'TBH', 'FROZEN')
) AS ed ON t.AD_ID = ed.AD_ID