SELECT *
FROM tablename
WHERE key = 12345
ORDER BY version;

##</code><code>##

SELECT *
FROM tablename
WHERE key LIKE '12345,%'
ORDER BY key;

##</code><code>##

SELECT *
FROM tablename o
WHERE key = ?
  AND version = (
        SELECT max(version)
        FROM tablename i
        WHERE i.key = o.key
)

##</code><code>##

SELECT *
FROM tablename
WHERE key = (
        SELECT max(key)
        FROM tablename
        WHERE key LIKE '$key,%'
)