SELECT statement where rows are omitted based on another table - sql

Question

Table with orders has another table with positions. I want the orders table to show but then only have the most up to-date position on it. Below is a picture of the 3 rows I want showing. Omit the rest.
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

Assuming that you want the row having the latest lastdateandtime for the truck name, this should work:
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')

Answer 2

If I understand correctly, you can get the most recent record for a truck using ROW_NUMBER():
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

Firstly, why are you using Truck002's name field rather than its id field as the link to DispacthTable? This is considered a less efficient way of doing it than using id (which is either a numerical field or a shorter string than name).
Secondly, you should mention in your Question that each Order can have many DispatchTable's and that each DispacthTable can have many Truck002's, otherwise many people will start by assuming that it is the other way round between DispatchTable and Truck002.
Thirdly, please try...
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 )
If you have any questions or comments, then please feel free to post a Comment accordingly.
Further Reading
https://msdn.microsoft.com/en-us/library/bb177906(v=office.12).aspx (on HAVING)
https://www.w3schools.com/sql/sql_having.asp (on HAVING)
https://msdn.microsoft.com/en-us/library/bb177905(v=office.12).aspx (on GROUP BY)
https://www.w3schools.com/sql/sql_groupby.asp (on GROUP BY)