Why does 9+1 = * , and how can I fix it? - sql-server

Question

I'm having trouble with my database because its got auditing worked in and things are hard. I need to compare the current change with the last change so I thought I'd include a grouping column. But when I run my code, some of the column values are . It goes 1,2,3,4,5,6,7,8,9, . What the ... idon'tevenknow ?
This is what I'm doing:
DECLARE #Person char(11), #DonationYTD decimal(10, 2), #OldPerson char(11), #OldDonationYTD decimal(10, 2), #Group int;
SET #Group=1;
DECLARE TempCursor CURSOR FOR Select PersonID, DonationYTD FROM MyTable;
OPEN TempCursor;
FETCH NEXT FROM TempCursor INTO #Person, #DonationYTD ;
WHILE ##FETCH_STATUS=0
BEGIN
IF( #Person != #OldPerson)
SET #Group=1;
IF( #Person = #OldPerson AND #DonationYTD!=#OldDonationYTD)
SET #Group=#Group+1;
UPDATE MyTable SET CHANGEGROUP=#Group WHERE PersonID=#Person AND DonationYTD=#DonationYTD;
SET #OldPerson = #Person;
SET #OldDonationYTD = #DonationYTD;
FETCH NEXT FROM TempCursor INTO #Person, #DonationYTD ;
END
CLOSE TempCursor;
DEALLOCATE TempCursor;
SELECT PersonID, DonationYTD, Changegroup FROM MyTable
1 15.00 1
1 15.00 1
1 20.00 1
2 3.00 1
2 4.00 2
2 15.00 3
2 8.00 4
2 4.00 5
2 15.00 6
2 3.00 7
2 3.00 7
2 9.00 8
2 9.00 8
2 10.00 9
2 14.00 *
2 14.00 *
If I try to do anything with Changegroup it tells me it can't convert varchar symbol * to integer.
Why am I getting an asterisk? How can I fix it?

Answer 1

You are encountering the issue described here
When integers are implicitly converted to a character data type, if
the integer is too large to fit into the character field, SQL Server
enters ASCII character 42, the asterisk (*).
From which I deduce your column must be [var]char(1). This odd behaviour does not occur for the newer n[var]char types, as discussed here.
The fix would be to change the column datatype. Ideally to a numeric datatype such as int but if it must be string at least one long enough to hold the intended contents.