SELECT语句，其中基于另一个表省略了行

Question

带有订单的表有另一个有仓位的表。我希望订单表显示，但只有最新的位置。下面是我想要显示的3行的图片。省略其余部分。

SELECT DispatchTable.ordernumber, DispatchTable.truck,
       DispatchTable.driver, DispatchTable.actualpickup, 
       DispatchTable.actualdropoff, orders.pickupdateandtime, 
       orders.dropoffdateandtime, Truck002.lastposition, 
       Truck002.lastdateandtime
FROM DispatchTable 
INNER JOIN orders ON DispatchTable.ordernumber = orders.id 
INNER JOIN Truck002 ON DispatchTable.truck = Truck002.name
WHERE (orders.status = 'onRoute')

Answer 1

假设您想要卡车name的最新SELECT DispatchTable.ordernumber, DispatchTable.truck, DispatchTable.driver, DispatchTable.actualpickup, DispatchTable.actualdropoff, orders.pickupdateandtime, orders.dropoffdateandtime, TruckLatest.lastposition, TruckLatest.lastdateandtime FROM DispatchTable INNER JOIN orders ON DispatchTable.ordernumber = orders.id INNER JOIN (SELECT name, lastposition, lastdateandtime FROM Truck002 Truck1 WHERE lastdateandtime = (SELECT MAX(lastdateandtime) FROM Truck002 Truck2 WHERE Truck2.name = Truck1.name)) TruckLatest ON DispatchTable.truck = TruckLatest.name WHERE (orders.status = 'onRoute') 行，这应该有效：

strto*()

Answer 2

如果我理解正确，您可以使用ROW_NUMBER()获取卡车的最新记录：

SELECT dt.ordernumber, dt.truck,
       dt.driver, dt.actualpickup, 
       dt.actualdropoff, o.pickupdateandtime, 
       o.dropoffdateandtime, t.lastposition, 
       t.lastdateandtime
FROM DispatchTable dt INNER JOIN
     orders o
     ON dt.ordernumber = o.id INNER JOIN
     (SELECT t.*,
             ROW_NUMBER() OVER (PARTITION BY t.name ORDER BY t.lastdateandtime DESC) as seqnum
      FROM Truck002 t
     ) t
     ON dt.truck = t.name
WHERE o.status = 'onRoute' AND seqnum = 1;

Answer 3

首先，您为什么使用Truck002的{​​{1}}字段而不是name字段作为id的链接？与使用DispacthTable（数字字段或比id更短的字符串）相比，这被认为是一种效率较低的方式。

其次，你应该在你的问题中提到每个name可以有很多Order个，并且每个DispatchTable可以有很多DispacthTable＆＃39 ; s，否则很多人会首先假设它是Truck002和DispatchTable之间的另一种方式。

第三，请尝试......

Truck002

如果您有任何问题或意见，请随时发表评论。

进一步阅读

https://msdn.microsoft.com/en-us/library/bb177906(v=office.12).aspx（SELECT DispatchTable.ordernumber, DispatchTable.truck, DispatchTable.driver, DispatchTable.actualpickup, DispatchTable.actualdropoff, orders.pickupdateandtime, orders.dropoffdateandtime, Truck002.lastposition, Truck002.lastdateandtime FROM DispatchTable INNER JOIN orders ON DispatchTable.ordernumber = orders.id INNER JOIN Truck002 ON DispatchTable.truck = Truck002.name WHERE (orders.status = 'onRoute') GROUP BY ordernumber HAVING lastdateandtime = MAX( lastdateandtime ) ）

https://www.w3schools.com/sql/sql_having.asp（HAVING）

https://msdn.microsoft.com/en-us/library/bb177905(v=office.12).aspx（HAVING）

https://www.w3schools.com/sql/sql_groupby.asp（GROUP BY）