[SvanteH]

Kanske slippa involvera PHP mer än nödvändigt?

(Otestat men bör fungera i teorin)

UPDATE newtable, 
       (SELECT id 
        FROM   table 
        WHERE  Rand() < 0.3) AS randIds 
SET    value = 'newvalue' 
WHERE  newtable.id = randIds.id