SELECT * FROM `ra_postmeta` WHERE `meta_key` = '_sale_price' AND `meta_value` > 0

_sale_price_dates_from >= 1406649975 AND _sale_price_dates_to <= 1406649975

SELECT * FROM `ra_postmeta`
WHERE (`meta_key` = '_sale_price' AND `meta_value` > 0)
AND (`meta_key` = '_sale_price_dates_to' AND ( `meta_value` >= 1406649975 OR `meta_value`=null))
AND (`meta_key` = '_sale_price_dates_from' AND ( `meta_value` <= 1406649975 OR `meta_value`=null))