SELECT c.*, b.v_s as mainPage, p.v_s as price FROM `catalog` c
LEFT JOIN `info` b ON c.id=b.id AND b.key='mainPage'
LEFT JOIN `info` p ON c.id=p.id AND p.key='price'
WHERE c.menu='Y'
ORDER BY p.v_s=`price`
SELECT c.*, b.v_s as mainPage, p.v_s as price FROM `catalog` c
LEFT JOIN `info` b ON c.id=b.id AND b.key='mainPage'
LEFT JOIN `info` p ON c.id=p.id AND p.key='price'
WHERE c.menu='Y'
ORDER BY `p`.`v_s`+0