SELECT DISTINCT在一列,返回多个其他列(SQL Server)

我正在尝试编写一个查询,从每个唯一设备的GPSReport表格返回最近的GPS位置.表中有50个设备,所以我只需要返回50行.

这是我到目前为止(不工作)

SELECT TOP(SELECT COUNT(disTINCT device_serial) FROM GPSReport) * FROM GPSReport AS G1
RIGHT JOIN
(SELECT disTINCT device_serial FROM GPSReport) AS G2
ON G2.device_serial = G1.device_serial
ORDER BY G2.device_serial,G1.datetime DESC

这返回50行,但是不返回每个device_serial的唯一行.它返回第一个设备的所有报告,然后返回第二个设备的所有报告等.

在一个查询中我正在尝试做什么？

解决方法

SELECT * FROM
GPSReport AS G1
JOIN (SELECT device_serial,max(datetime) as mostrecent 
      FROM GPSReport group by device_serial) AS G2
ON G2.device_serial = G1.device_serial and g2.mostrecent = g1.datetime
ORDER BY G1.device_serial

原文地址：https://www.jb51.cc/mssql/81964.html