mysql order by排序查询速度问题

SELECT * FROM `assets_message` LEFT JOIN purchase_message ON assets_message.purchase_id = purchase_message.purchase_id 
WHERE  `purchase_type` = 'oassets'AND purchase_message.assets_type = '002'
ORDER BY purchase_message.purchase_id,assets_id

SELECT * FROM `assets_message` LEFT JOIN purchase_message ON assets_message.purchase_id = purchase_message.purchase_id 
WHERE  `purchase_type` = 'oassets' AND purchase_message.assets_type = '002'
ORDER BY assets_message.purchase_id,assets_id

未完待续……