Which solution you think is best to use as fastest method:
Method 1:
$db->query("SELECT id, title, date, alt_name, short_story, rating, news_read FROM " . PREFIX . "post WHERE approve='$conf[allow_index_metka]' AND category regexp '[:<:][[:>:]]' AND id >= (SELECT MIN(id) + ROUND( ( MAX(id)-MIN(id) ) * RAND() ) FROM " . PREFIX . "post ) ORDER BY id LIMIT 4");
Method 2:
$db->query("SELECT id, title, date, alt_name, short_story, rating, news_read FROM " . PREFIX . "post WHERE approve='$conf[allow_index_metka]' AND category regexp '[:<:][[:>:]]' AND id >= (SELECT FLOOR( MAX(id) * RAND()) FROM " . PREFIX . "post ) ORDER BY id LIMIT 4");
or to use something else perhaps?