MySQL: Lücken in fortlaufenden Nummern finden

Mal wieder ein nützliches MySQL-Schnipsel.

SELECT a AS id, b AS next_id, (b - a) -1 AS missing_inbetween 
FROM (

    SELECT a1.id AS a , MIN(a2.id) AS b 
    FROM my_table  AS a1
    LEFT JOIN my_table AS a2 ON a2.id > a1.id
    WHERE a1.id <= 100
    GROUP BY a1.id
    ) AS tab

WHERE b > a + 1