Insert uniqueidentifier value to new table - sql-server

Question

SQL Server 2008
I have a table with 2 fields among others
TableA
alterid uniqueidentifier
revnum varchar(50)
Another table has the exact fields as the first one
TableB
alterid uniqueidentifier
revnum varchar(50)
I want to check compare the revnum fields. For each record of TableA I check if there is a record in TableB. If it exists and the revnum fields are different I update the TableB.revnum to the TebleA.revnum. If it does not exist then I add the record from TableA to TableB.
Here is the code
BEGIN
SET #Prod_curs =CURSOR FOR SELECT s.alterid, s.revnum, r.revnum FROM TableA s LEFT OUTER JOIN
TableB r ON s.alterid=r.alterid
WHERE s.revnum<>r.revnum OR r.revnum IS NULL
OPEN #Prod_curs
FETCH NEXT FROM #Prod_curs INTO #alterid, #srevnum, #rrevnum
WHILE ##FETCH_STATUS=0
BEGIN
IF #rrevnum IS NULL
BEGIN
INSERT INTO TableB (alterid,revnum) VALUES (#alterid,ISNULL(#srevnum,0))
END
IF #srevnum<>#rrevnum
BEGIN
UPDATE TableB SET revnum=#srevnum WHERE alterid=#alterid
END
FETCH NEXT FROM #Prod_curs INTO #alterid, #srevnum, #rrevnum
END
CLOSE #Prod_curs;
DEALLOCATE #Prod_curs;
END
My code works fine in a set of about 15000 records except some records where a weird thing happens.
In TableA I have this record
alterid revnum
'A770B280-B4DA-4937-9046-B24E60259AB6' '2-414922-1--1-1-2-51-0'
When it is store in TableB the values are
alterid revnum
'BF18A0EB-A684-486B-B053-55BC2969F1E3' '2-414922-1--1-1-2-51-0'
For some reason the alterid changes and I can't figure out why.
Can someone help

Answer 1

seems like code is working fine its just select that you are doing after insert/update.
i do have some unclear thing in your post as well.
Does the column "revnum" is primary key or has unique constraint on it in TableB ?
the result you have shown what is the select stmt you use for TableB ?
was it something like "Select top 1 * from TABLEB where revnum=xyz" ?
i ran you logic on dummy data and update/insert is fine.
check this code. what i doubt is in TABLEB you already have some "AlterID" with same "rvnum" value that is not present in "TableA"
see the below result where instead (3,3) i am also seeing (4,3)
SET NOCOUNT ON
DECLARE #t1 TABLE
(
id INT
,VALUE INT
)
INSERT INTO #t1 ( id, VALUE )
SELECT 1,1 UNION ALL SELECT 2,2 UNION ALL SELECT 3,3
DECLARE #t2 TABLE
(
id INT
,VALUE INT
)
INSERT INTO #t2 ( id, VALUE )
SELECT 1,1 UNION ALL SELECT 2,2 UNION ALL SELECT 4,3
DECLARE #Value1 INT,#Value2 INT,#ID INT ,#Prod_curs CURSOR
SET #Prod_curs =CURSOR FOR
SELECT s.id, s.Value, r.value
FROM #t1 s LEFT OUTER JOIN
#t2 r ON s.id=r.ID
WHERE s.Value<>r.Value OR r.Value IS NULL
OPEN #Prod_curs
FETCH NEXT FROM #Prod_curs INTO #ID, #Value1, #Value2
WHILE ##FETCH_STATUS=0
BEGIN
IF #Value2 IS NULL
BEGIN
INSERT INTO #T2 (ID,Value) VALUES (#ID,ISNULL(#Value1,0))
END
IF #Value1<>#Value2
BEGIN
UPDATE #T2 SET Value=#Value2 WHERE ID=#ID
END
FETCH NEXT FROM #Prod_curs INTO #ID, #Value1, #Value2
END
CLOSE #Prod_curs;
DEALLOCATE #Prod_curs;
SELECT TOP 1 * FROM #t2 WHERE VALUE = 3