maybe this can help you
SELECT *
FROM giper
WHERE `name` LIKE '%$search%' OR `art` LIKE '$search%'
ORDER BY `art`, `name`
LIMIT 20
or
SELECT *
FROM giper
WHERE if ('$search'=0 ,`name` LIKE '%$search%' , `art` LIKE '$search%')
ORDER BY `art`, `name`
LIMIT 20