mysql - 递归 SQL 查询。选择最后一个条目分组方式

Question

我有一个价格表，其中包含此价格的目的地、价格和有效日期。

我想获得一个包含最新价格的目的地列表。

示例表：

Destination  | Code | Effective_date | Price
Spain        | 34   | 2013-04-05     | 0.02
Spain        | 34   | 2013-07-01     | 0.01
Spain Mobile | 346  | 2013-04-05     | 0.07
Spain Mobile | 346  | 2013-07-01     | 0.08

例如，如果我搜索代码 34，我想获得 Spain 2013-07-01 和 Spain Mobile 2013-07-01 我尝试使用

SELECT * 
FROM carrier_fares AS cf1               
WHERE NOT EXISTS (
    SELECT * FROM carrier_fares AS cf2
    WHERE code LIKE ?
    AND cf1.effective_date < cf2.effective_date
    )

该表有超过 50.000 个条目。

Answer 1

   SELECT x.*
     FROM carrier_fares x
     JOIN  
        ( SELECT destination
               , MAX(effective_date) max_date 
            FROM carrier_fares 
           GROUP 
              BY destination
        ) y
       ON y.destination = x.destination 
      AND y.max_date = x.effective_date

-- [WHERE code LIKE '34%']
;

Answer 2

SELECT * FROM (
   SELECT * FROM carriers_fares ORDER BY effective_date DESC
) as t1 GROUP by effective_date, code