MySQL: get differences of each sorted column in set of rows

CREATE TABLE characters_by_gametime (
  id INTEGER AUTO_INCREMENT PRIMARY KEY,
  gold INTEGER,
  live INTEGER);

INSERT INTO characters_by_gametime (gold, live)
SELECT gold, live
FROM characters
ORDER BY game_time;

SELECT
  c1.id,
  c1.gold - IFNULL(c2.gold, 0) AS gold,
  c1.live - IFNULL(c2.live, 0) AS live
FROM
  characters_by_gametime c1
  LEFT JOIN characters_by_gametime c2
    ON c1.id = c2.id + 1
ORDER BY
  c1.id;

GameID      CharacterName GameTime    Gold        Live
----------- ------------- ----------- ----------- -----------
1           Foo           10          100         3
2           Foo           20          100         2
3           Foo           30          95          2

SELECT
    c.CharacterName,
    CASE WHEN c_offset.Gold IS NOT NULL THEN c.Gold - c_offset.Gold ELSE c.Gold END AS Gold,
    CASE WHEN c_offset.Live IS NOT NULL THEN c.Live - c_offset.Live ELSE c.Live END AS Live
FROM Characters c
    LEFT OUTER JOIN Characters c_offset
    	ON c.GameID - 1 = c_offSet.GameID
ORDER BY
    c.GameTime

CharacterName Gold        Live
------------- ----------- -----------
Foo           100         3
Foo           0           -1
Foo           -5          0