GROUP result value if null

Question

I can't do this query :

TABLE:

------------
NOTES  | TOTAL
------------
NULL    |  23
NULL    |  12
pay1    | -13
pay2    | -23
-------------

RESULTS :

------------
NOTES   | TOTAL
------------
SELL    |  35
pay1    | -13
pay2    | -23
-------------

I need sum all NULL fields and group with the name " SELL ".

Answer 1

select IFNULL(NOTES,'SELL') n,SUM(TOTAL) FROM records GROUP BY n;

Answer 2

Check the name column which as NULL value using IF conditional statement and replace with "SELL" text.

select IF(name is  NULL, "SELL", name) as name, sum(total) as total from content group by name;

Answer 3

SELECT 
IFNULL(NOTES,'SELL')as NOTES,
SUM(TOTAL)  as TOTAL
FROM records 
GROUP BY notes
ORDER BY IFNULL(NOTES,'a')