mysql - 在 MySQL 中，我如何通过不同的列和公用键按日期获取最新记录？

Question

我有一个类似这样的数据集:

id   product_id   size       color     price   created_date
------------------------------------------------------------------
1    24           small      black     9.99    2012-06-21 00:00:00
2    24           small      red       9.99    2012-06-23 00:00:00
3    24           medium     black     11.99   2012-06-24 00:00:00
4    24           medium     red       11.99   2012-06-24 00:00:00
5    24           large      black     12.99   2012-06-25 00:00:00
6    24           large      red       12.99   2012-06-26 00:00:00
7    24           small      black     8.99    2012-06-27 00:00:00
8    24           medium     black     10.99   2012-06-29 00:00:00
9    24           large      red       13.99   2012-06-30 00:00:00
10   24           medium     red       10.99   2012-07-01 00:00:00

我预期的结果集是:

id   product_id   size       color     price   created_date
------------------------------------------------------------------
2    24           small      red       9.99    2012-06-23 00:00:00
5    24           large      black     12.99   2012-06-25 00:00:00
7    24           small      black     8.99    2012-06-27 00:00:00
8    24           medium     black     10.99   2012-06-29 00:00:00
9    24           large      red       13.99   2012-06-30 00:00:00
10   24           medium     red       10.99   2012-07-01 00:00:00

换句话说，从 product_id = 24 和 size/color 唯一的表中选择所有并且只返回 created_date 的最新条目。

我不确定解决此问题的最佳方法是什么。通过临时表子选择？内部联接？某种独特/独特的组合？我可能让这比它必须的更困难。

Answer 1

您需要获得 groupwise maximum :

SELECT   mytable.*
FROM     mytable NATURAL JOIN (
  SELECT   size, color, MAX(created_date) AS created_date
  FROM     mytable
  GROUP BY size, color
) AS t

查看 sqlfiddle .