Executing SP inside while loop works only first time - sql-server

Question

In SQL Server 2012, I have a script that call a stored procedure multiple times.. The loop will be executed as many times as the number of records in [ResultHeader] table.
EXEC [AS400].tp_SelectChildItems #Pgm, #Grp, #Pgmgrpseq,
null, null, null, null, null, #ItemSelection, null,
null, null, null, null,
Note: This SP has a table variable inside
I have a comma separated list of SelectedCostPageList. For each value in this list, the loop is executed once.
I am observing a weird behavior. When I invoke the sp from the script, only for the first time the sp is returning proper records.. On subsequent calls the stored procedure is returning no records. Very odd…. When I change the order of comma separated string, only for the first iteration the sp is returing records.. other times no records.
Any guess what will be the reason?
DECLARE #SelectedCostPageList VARCHAR(MAX)
SET #SelectedCostPageList = (SELECT (SELECT CONVERT(VARCHAR(32), A.PGM + '-'+A.GRP+'-'+A.PGMGRPSEQ) + ', ' AS [text()]
FROM dbo.[ResultHeader] A
WHERE UserId = 'U25703'
FOR XML PATH('')) AS CostPages) ResultHeader
PRINT #SelectedCostPageList
DECLARE #pos INT
DECLARE #len INT
set #pos = 0
set #len = 0
DELETE FROM ResultItems
WHILE CHARINDEX(',', #SelectedCostPageList, #pos+1)>0
BEGIN
set #len = CHARINDEX(',', #SelectedCostPageList, #pos+1) - #pos
DECLARE #SelectedCostPage VARCHAR(10)
set #SelectedCostPage = SUBSTRING(#SelectedCostPageList, #pos, #len)
set #pos = CHARINDEX(',', #SelectedCostPageList, #pos+#len) +1
PRINT #SelectedCostPage
DECLARE #Pgm AS VARCHAR (10);
DECLARE #Grp AS VARCHAR (10);
DECLARE #Pgmgrpseq AS VARCHAR (10);
SELECT #Pgm = (SELECT VALUE
FROM [AS400].[tf_SelectSplitString] (#SelectedCostPage, '-')
WHERE POSITION = 1);
PRINT #Pgm
SELECT #Grp = (SELECT VALUE
FROM [AS400].[tf_SelectSplitString] (#SelectedCostPage, '-')
WHERE POSITION = 2);
PRINT #Grp
SELECT #Pgmgrpseq = (SELECT VALUE
FROM [AS400].[tf_SelectSplitString] (#SelectedCostPage, '-')
WHERE POSITION = 3);
PRINT #Pgmgrpseq
Declare #ItemSelection as varchar(4000)
set #ItemSelection ='1116102540,1116102541';
print #ItemSelection
print 'HAI'
print #Pgmgrpseq
EXEC [AS400].tp_SelectChildItems
#Pgm, #Grp, #Pgmgrpseq,
null, null, null,
null, null, #ItemSelection, null,
null, null, null, null,
null, null, null, 1, 'U25703'
END
SELECT * FROM ResultItems
WHERE UserId = 'U25703'

Answer 1

If I had to guess, it would be because you are using ', ' (comma followed by a space) as a list separator, but the code is just looking for a comma. You would then have a leading space on a string value, which, presumably, would not then match whatever needs to be matched.
The first works, because you initialize the list string with a comma without a space.
Perhaps more importantly, I find the approach of stuffing things into a string to loop over them to be, shall I say, very 1980s. You could use a cursor (not my favorite approach) or a temporary table. When I want to do loops over such data, I sometimes structure them as follows:
declare #looptable table (rownum int identity(1, 1), . . . );
insert into #looptable . . .;
declare #tot int;
select #tot = count(*) from #looptable;
declare #i int = 1;
while (#i <= tot)
begin
-- something here with "where rownum = #i"
end;
The idea of stuffing values into a string just to write more code to parse them out seems like a waste of programming effort. In addition, this can cause problems because of the conversion of types into character formats and the obscene ways that for path xml handles characters such as '<' and '>'.