仅获得每天多个条目中的最后一行

Question

我陷入了试图在查询中整理一天中最后一个条目的问题，每个实体我都会得到24行。 我已经在这篇文章中阅读了与解决方案非常相似的问题，但是我无法将其合并到现有查询中。

我现有的查询：

SELECT distinct b.Udc_id as EAN, sax.attrib_01, c.channel_no, a.local_read_time, a.read, a.Status
from register_reads a, lookup_mv_channels1 c, lookup_mv_sdps b
LEFT outer JOIN s_asset@mudr2sebl sa
 ON sa.x_udc_asset_id = b.Udc_id
LEFT outer JOIN s_asset_xm@mudr2sebl sax
 ON sax.par_row_id = sa.row_id
WHERE c.Channel_id = a.channel_id
AND b.meter_id = c.meter_id
AND sax.attrib_02 = 'Y'
AND a.local_read_time >= (SYSDATE) - 1
order by b.Udc_id, a.local_read_time

由此产生的结果例如是：

||EAN | ATTRIB_01 | channel_no | LOCAL_READ_TIME   | READ | STATUS||
||1234| ready     |     1      |09/11/2015 01:00:01|     0|  val  ||
||1234| ready     |     1      |09/11/2015 02:00:01|    10|  val  ||
||1234| ready     |     1      |        ...        |   ...|  val  ||
||1234| ready     |     1      |09/11/2015 23:59:01|    60|  val  ||
||3456| ready     |     1      |09/11/2015 01:00:01|   204|  val  ||
||3456| ready     |     1      |        ...        |   ...|  val  ||
||3456| ready     |     1      |09/11/2015 23:58:01|   400|  val  ||

我想要达到的结果是：

||EAN | ATTRIB_01 | channel_no | LOCAL_READ_TIME   | READ | STATUS||
||1234| ready     |     1      |09/11/2015 23:59:01|    60|  val  ||
||3456| ready     |     1      |09/11/2015 23:58:01|   400|  val  ||

从@levelonehuman反馈后更改：

SELECT  b.Udc_id as EAN, 
        c.physical_channel_no, 
        a.local_read_time, 
        a.cum_read, 
        a.validation_Status
FROM register_reads a, lookup_mv_channels1 c, lookup_mv_sdps b
    INNER JOIN (SELECT  b.Udc_id, 
                        MAX(a.LOCAL_READ_TIME) AS LOCAL_READ_TIME
               FROM    register_reads, lookup_mv_sdps b
               GROUP BY b.Udc_id) AS t2
    ON b.Udc_id = t2.Udc_id AND b.LOCAL_READ_TIME = t2.LOCAL_READ_TIME
;

Answer 1

注意：这是用于MSSQL

您需要为其他任何表添加其他联接，但是您可以使用MAX(LOCAL_READ_TIME)和GROUP BY EAN获得最后一行：

SELECT  EAN, 
        ATTRIB_01, 
        channel_no, 
        LOCAL_READ_TIME, 
        READ, 
        STATUS
FROM    TableName t1
    INNER JOIN (    SELECT  EAN, 
                            MAX(LOCAL_READ_TIME) AS LOCAL_READ_TIME
                    FROM    TableName
                    GROUP BY EAN
    ) AS t2 ON t1.EAN = t2.EAN AND t1.LOCAL_READ_TIME = t2.LOCAL_READ_TIME

INNER JOIN部分将选择TableName上具有EAN和MAX(LOCAL_READ_TIME) -然后，您将MAX(LOCAL_READ_TIME)回到TableName （同一张表）以根据JOIN标准选择其余数据。

有效地，这将筛选出不符合EAN + MAX(LOCAL_READ_TIME)标准的行。