MySQL查询选择最大值

Question

我有两张桌子：

product
id | name
1  |  A
2  |  B

history
id_product | year | month | percent
1          | 2014 |   2   |  0
1          | 2014 |   3   |  20
1          | 2014 |   4   |  60

如果月份是当前月份或前一个月，我如何获得最高百分比，例如：

SELECT * FROM history 
WHERE id_product IN
     (SELECT id FROM product 
      WHERE id = 1) 
  AND ((year = 2014 AND month = 3) OR 
       (year = 2014 AND month = 2)) 
ORDER BY year DESC, month DESC

这会输出：20但它实际上显示0，它总是给我一个月前的价值...欢迎任何建议......谢谢!!

Answer 1

SELECT max(hs.`percent`) as `percent`, hs.id_product, p.name FROM
(SELECT * 
FROM history 
WHERE ((year = 2014 AND month = 3) OR 
       (year = 2014 AND month = 2)) 
) as hs
LEFT JOIN `product` as p on p.id=hs.id_product
GROUP BY hs.id_product

试试这个。