DECLARE @strng varchar(max) = 'bzz';
DECLARE @strngOut varchar(max) = '';
DECLARE @incremented bit = 1;
SET @strng = REVERSE(@strng);
SELECT @strngOut = @strngOut + CHAR(CASE WHEN n.Number + @incremented = 26 THEN 0 ELSE n.Number
+ @incremented END + 97), @incremented = CASE WHEN n.Number + @incremented = 26 THEN 1 ELSE 0 END
FROM (
SELECT (CAST(ASCII(substring(@strng, v.number+1, 1)) AS int) - 97) AS Number
FROM master..spt_values v
WHERE v.type = 'P' AND v.number < len(@strng)
) n;
IF (@incremented = 1)
BEGIN
SET @strngOut = @strngOut + 'a';
END
SELECT REVERSE(@strngOut)