如何显示不同的记录，我想检查：如果表中已经存在blueid，则该数据仅在特定日期显示一次

Question

表名称：发现的设备

+-----------+--------------+------+-----+-------------------+----------------+
| Field     | Type         | Null | Key | Default           | Extra          |
+-----------+--------------+------+-----+-------------------+----------------+
| id        | int(100)     | NO   | PRI | NULL              | auto_increment |
| blueid    | varchar(250) | NO   |     | NULL              |                |
| scannerid | varchar(250) | NO   |     | NULL              |                |
| datetime  | datetime     | NO   |     | CURRENT_TIMESTAMP |                |
+-----------+--------------+------+-----+-------------------+--------------


+--------------+--------------------------+---------------------+
| blueid       | scannerid                | datetime            |
+--------------+--------------------------+---------------------+
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 10:40:20 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 10:45:16 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 10:50:14 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 10:55:15 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 11:05:21 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 11:10:15 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 11:15:22 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 11:20:17 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 11:25:18 |
| Galaxy Note3 | CIS5040 Raspberry Device | 2017-04-07 11:30:17 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 11:50:17 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 11:55:16 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:18:16 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:20:15 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:27:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:28:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:29:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:30:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:31:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:32:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:33:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:34:19 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:35:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:36:14 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:38:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:39:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:40:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:41:15 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:42:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:43:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:44:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:45:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:46:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:47:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:48:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:49:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:50:19 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:51:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:52:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:53:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:54:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:55:19 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:56:20 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:57:17 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:58:19 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 12:59:17 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:00:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:01:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:02:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:03:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:04:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:06:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:07:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:08:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:09:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:10:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:11:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:12:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:13:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:14:19 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:15:17 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:16:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:17:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:18:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:19:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:20:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:21:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:22:19 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:23:14 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:24:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:25:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:26:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:27:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:28:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:29:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:31:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:32:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:33:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:35:19 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:36:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:37:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:38:19 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:39:12 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:40:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:41:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:42:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:43:14 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:44:18 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:45:13 |
| yuviandroid  | CIS5040 Raspberry Device | 2017-04-07 13:47:17 |
+--------------+--------------------------+---------------------+

我用这个查询

SELECT DISTINCT `blueid`,`scannerid`,`datetime`
FROM discovereddevices
WHERE date(datetime) = CURRENT_DATE.

现在，如何才能在特定日期仅获取一次类似于yuviandroid的值。 当前，考虑到时间，数据显示出不同的值。 有人可以对此提出建议。

Answer 1

如果不想，为什么还要加上日期？

SELECT DISTINCT blueid, scannerid
FROM discovereddevices
WHERE date(datetime) = CURRENT_DATE;

Answer 2

此查询将返回每个blueid的最大日期时间：

select blueid, max(datetime) as max_dt
from discovereddevices
where date(datetime) = CURRENT_DATE
group by blueid, date(datetime)

并且此查询将返回与上一个datetime相关的所有其他列：

select d.*
from
  discovereddevices d inner join (
    select blueid, max(datetime) as max_dt
    from discovereddevices
    where date(datetime) = CURRENT_DATE
    group by blueid
  ) l on d.blueid = l.blueid and d.datetime = l.max_dt