sql 筛选每个ID的最新数据(根据创建时间排序 筛选最新的数据

需求：筛选出数据表中每个user_id的最新记录。

解决方法：根据分组获取 ID , max(时间) 函数获取最大的创建时间 ，根据时间和ID获取需要的对应记录 。

例如：

truncate table comment;

INSERT INTO `comment` (`id`, `user_id`, `content`, `addtime`, `lastmodify`) VALUES

(1, 1, '评论1', '2017-05-17 00:00:00', '2017-05-17 00:00:00'),

(2, 1, '评论2', '2017-05-17 00:10:01', '2017-05-17 00:10:01'),

(3, 2, '评论1', '2017-05-17 00:10:02', '2017-05-17 00:10:02'),

(4, 2, '评论2', '2017-05-17 00:00:03', '2017-05-17 00:00:03'),

(5, 3, '评论1', '2017-05-17 00:10:04', '2017-05-17 00:10:04'),

(6, 1, '评论3', '2017-05-17 00:00:05', '2017-05-17 00:00:05'),

(7, 4, '评论1', '2017-05-17 00:00:06', '2017-05-17 00:00:06'),

(8, 4, '评论2', '2017-05-17 00:10:07', '2017-05-17 00:10:07'),

(9, 4, '评论3', '2017-05-17 00:00:08', '2017-05-17 00:00:08'),

(10, 4, '评论4', '2017-05-17 00:00:09', '2017-05-17 00:00:09'),

(11, 3, '评论2', '2017-05-17 00:00:10', '2017-05-17 00:00:10');

select * from comment;

+----+---------+---------+---------------------+---------------------+

| id | user_id | content | addtime            | lastmodify          |

+----+---------+---------+---------------------+---------------------+

|  1 |      1 | 评论1  | 2017-05-17 00:00:00 | 2017-05-17 00:00:00 |

|  2 |      1 | 评论2  | 2017-05-17 00:10:01 | 2017-05-17 00:10:01 |

|  3 |      2 | 评论1  | 2017-05-17 00:10:02 | 2017-05-17 00:10:02 |

|  4 |      2 | 评论2  | 2017-05-17 00:00:03 | 2017-05-17 00:00:03 |

|  5 |      3 | 评论1  | 2017-05-17 00:10:04 | 2017-05-17 00:10:04 |

|  6 |      1 | 评论3  | 2017-05-17 00:00:05 | 2017-05-17 00:00:05 |

|  7 |      4 | 评论1  | 2017-05-17 00:00:06 | 2017-05-17 00:00:06 |

|  8 |      4 | 评论2  | 2017-05-17 00:10:07 | 2017-05-17 00:10:07 |

|  9 |      4 | 评论3  | 2017-05-17 00:00:08 | 2017-05-17 00:00:08 |

| 10 |      4 | 评论4  | 2017-05-17 00:00:09 | 2017-05-17 00:00:09 |

| 11 |      3 | 评论2  | 2017-05-17 00:00:10 | 2017-05-17 00:00:10 |

+----+---------+---------+---------------------+---------------------+

根据上面的表格字段进行sql语句的查询。

select a.* from comment as a right join 

(select user_id, max(addtime) as maxtime from comment where user_id is not null group by user_id) as b 

on a.user_id=b.user_id and a.addtime=b.maxtime order by a.user_id asc;

+------+---------+---------+---------------------+---------------------+

| id   | user_id | content | addtime             | lastmodify          |

+------+---------+---------+---------------------+---------------------+

|    2 |       1 | 评论2   | 2017-05-17 00:10:01 | 2017-05-17 00:10:01 |

|    3 |       2 | 评论1   | 2017-05-17 00:10:02 | 2017-05-17 00:10:02 |

|    5 |       3 | 评论1   | 2017-05-17 00:10:04 | 2017-05-17 00:10:04 |

|    8 |       4 | 评论2   | 2017-05-17 00:10:07 | 2017-05-17 00:10:07 |

+------+---------+---------+---------------------+---------------------+

上面则会出呈现出每个人的最新记录。