Question

我有2个表要使用，我希望显示结果，具体取决于table2中所有者Table1 ='ownerA'中的最新数据：表1：

    # id,    name,           owner
________________________________________________
    19782, device1,        ownerA
    19783, device8,        ownerB
    19784, device2,        ownerA
    19785, device3,        ownerA

表2：

# nasid, sim, timestamp
_______________________________________
19782, 0, 2015-12-08 15:34:27
19782, 0, 2015-12-08 15:34:33
19772, 0, 2015-12-08 15:34:39
19752, 0, 2015-12-08 15:34:45
19783, 0, 2015-12-08 15:34:50
19712, 0, 2015-12-08 15:34:56
19783, 0, 2015-12-08 15:35:02
19782, 0, 2015-12-08 15:35:07
19784, 0, 2015-12-08 15:35:13
19784, 0, 2015-12-08 15:35:20

我想要输出的内容：

# name, nasid, sim,     timestamp
_______________________________________
device8, 19783, 0, 2015-12-08 15:35:02
device1, 19782, 0, 2015-12-08 15:35:07
device2, 19784, 0, 2015-12-08 15:35:20

这就是我尝试过的，：

select nasid, sim, MAX(timestamp) 
from Table1 T1,Table2 T2
where 
Table1.owner='ownerA' 
and
T2.timestamp = (SELECT MAX(T2_2.timestamp)
                    FROM Table2 T2_2
                    WHERE T2.sim=T2_2.sim)

这是我的SHOw CREATE：表1：

CREATE TABLE `Table1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(64) COLLATE latin1_general_ci DEFAULT NULL,
  `owner` varchar(128) COLLATE latin1_general_ci DEFAULT '',
  UNIQUE KEY `name` (`name`),
  KEY `id` (`id`),
  KEY `owner` (`owner`),
) ENGINE=InnoDB AUTO_INCREMENT=26696 DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci

表2：

CREATE TABLE `Table2` (
  `nasid` int(11) DEFAULT NULL,
  `sim` char(20) COLLATE latin1_general_ci DEFAULT NULL,
  `timestamp` datetime DEFAULT NULL,
  KEY `nasid` (`nasid`),
  KEY `timestamp` (`timestamp`),
  KEY `sim` (`sim`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci

Answer 1

通常我会生成一个包含最大值和唯一键的数据集，然后将其简单地连接回包含我们需要的其他数据的基本集。

SELECT T1.name, T2.nasid, T2.sim, T2.timestamp
FROM Table1 T1
INNER JOIN table2 T2
 on T1.ID = T2.nasid
INNER JOIN (SELECT max(timestamp) mt, nasid 
            FROM table2 
            GROUP BY  nasid) A
   on A.MT = T2.TimeStamp
  and A.Nasid = T2.Nasid
WHERE T1.Owner = 'ownerA'

好吧，让我们回到原始查询...

我认为你所有的错误都是sim应该是无效的。因为sim dons似乎是表格的关键。只有基于所提供数据的nasid和时间戳才会生成唯一密钥。你和你错过了t1和t2之间的联接。

select name, nasid, sim, timestamp
from Table1 T1,Table2 T2
where Table1.owner='ownerA' 
and T1.Id = t2.nasid
and T2.timestamp = (SELECT MAX(T2_2.timestamp)
                    FROM Table2 T2_2
                    WHERE T2.nasid=T2_2.nasid)

Answer 2

经过很长一段时间，这就是让它更快的原因：

SELECT name, nasid, sim,  max(timestamp)
FROM Table1, Table2
WHERE Owner = 'OwnerA'
and id = nasid 
GROUP BY  nasid

MySQL显示2个表中的行，表2中包含最新数据

2 个答案: