SQL Server 最大日期时间

Question

I am a bit new to SQL Server and I am trying to execute a really simple query that goes like:

SELECT 
    ProductID, o.OrderID, o.CustomerID, CompanyName,OrderDate, Quantity
FROM  
    o 
JOIN 
    [Order Details] od on o.OrderID = od.OrderID
JOIN
    Customers c on c.CustomerID = o.CustomerID
WHERE
    orderdate = (select max(OrderDate)  
                 from o
                 where ProductID = od.ProductID)

And then I got this.

ProductID        OrderID        CustomerID        CompanyName        OrderDate        Quantity
2        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        24
3        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        4
4        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        1
6        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        1
7        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        1
8        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        2
10        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        1
12        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        2
13        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        4
14        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        1
16        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        2
20        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        1
23        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        2
32        11077        RATTC        Rattlesnake Canyon Grocery        1998-05-07 09:50:47.000        1

but I want to get the newest orderdate for every productID. Like this:

So what should I do to get that?

Answer 1

This should get you started. I'm assuming that Order Details has order line items.

SELECT
   p.ProductID,
   o.OrderID,
   o.CustomerID,
   o.CompanyName,
   o.OrderDate
FROM
    dbo.Products p
    CROSS APPLY (
        SELECT TOP 1 *
        FROM dbo.Orders o
        WHERE EXISTS (
           SELECT *
           FROM dbo.[Order Details] od
           WHERE
              o.OrderID = od.OrderID
              AND p.ProductID = od.ProductID
        )
        ORDER BY o.OrderDate DESC
    ) o
    INNER JOIN dbo.Customers c
       ON o.CustomerID = c.CustomerID
;

I assumed that [Order Details] rows can have the same OrderID twice, which makes things a bit more complicated to get the Quantity (which I left out). Would you want that quantity summed, or to show two rows? Depending on what result you want and how that table is implemented, this could be the solution you want:

SELECT
   p.ProductID,
   odq.OrderID,
   odq.CustomerID,
   odq.CompanyName,
   odq.OrderDate,
   odq.Quantity
FROM
    dbo.Products p
    CROSS APPLY (
        SELECT TOP 1 *
        FROM dbo.Orders o
        CROSS APPLY (
           SELECT TotalQuantity = Sum(Quantity)
           FROM dbo.[Order Details] od
           WHERE
              o.OrderID = od.OrderID
              AND p.ProductID = od.ProductID
        ) odq
        ORDER BY o.OrderDate DESC
    ) odq
    INNER JOIN dbo.Customers c
       ON o.CustomerID = c.CustomerID
;

This query should perform well as long as you have appropriate indexes on your tables ( Order Details should have index ProductID, OrderID and Orders should have an index starting with ProductID, OrderDate ). Its performance should remain steady as the system's data grows.

I did assume that you have a dbo.Products table, and by changing from CROSS APPLY to OUTER APPLY (the first one), you can show products that have no orders. Alternately, there's another possible query:

WITH OrderSequences AS (
   SELECT
      Sequence = Rank() OVER (PARTITION BY od.ProductID ORDER BY o.OrderDate DESC),
      o.*,
      od.ProductID,
      od.Quantity
   FROM
      dbo.Orders o
      INNER JOIN dbo.[Order Details] od
         ON o.OrderID = od.OrderID
)
SELECT
   o.OrderID,
   o.CustomerID,
   o.CompanyName,
   o.OrderDate,
   o.ProductID,
   o.Quantity
FROM
   OrderSequences o
   INNER JOIN dbo.Customers c
      ON o.CustomerID = c.CustomerID
WHERE
   Sequence = 1
;

Again, if you can have the same OrderID on more than one line in an order (a very likely thing in my opinion), then you'll need to do some kind of summing, or tolerate the duplicate rows that this will generate (as it will show BOTH rows on the same order if they were, together, the last time that ProductID was ordered).

This second query is likely to get slower and slower as the system ages and accumulates data, because it is forced to perform the windowing function on every row in the entire table (it can never be sure it has found the highest date and has found every ProductID until the end).

Answer 2

WITH X AS 
(SELECT ProductID
      , o.OrderID
      , o.CustomerID
      , CompanyName
      ,OrderDate
      , Quantity
      ,ROW_NUMBER() OVER (PARTITION BY od.productid ORDER BY o.OrderDate DESC) rn 
FROM [Orders] o 
JOIN [Order Details] od on o.OrderID = od.OrderID
join Customers c        on c.CustomerID=o.CustomerID
)
SELECT  ProductID
      , OrderID
      , CustomerID
      , CompanyName
      , OrderDate
      , Quantity
FROM X
WHERE rn = 1

OR

SELECT  ProductID
      , OrderID
      , CustomerID
      , CompanyName
      , OrderDate
      , Quantity
FROM 
(SELECT ProductID
      , o.OrderID
      , o.CustomerID
      , CompanyName
      ,OrderDate
      , Quantity
      ,ROW_NUMBER() OVER (PARTITION BY od.productid ORDER BY o.OrderDate DESC) rn 
FROM [Orders] o 
JOIN [Order Details] od on o.OrderID = od.OrderID
join Customers c        on c.CustomerID=o.CustomerID
)x
WHERE rn = 1

Answer 3

Using MAX(OrderDate) in a subquery, there is nothing to correlate the max(date) with the productID in the parent query. So you will always get all orders that have the Max(Date) of the first ProductID from the Order-Product join.

The best way to do this kind of filter is to join the o order table to itself.

SELECT ProductID, o.OrderID, o.CustomerID, CompanyName,OrderDate, Quantity
FROM  o 

LEFT JOIN o2 ON o.ProductID = o2.ProductID AND o2.OrderDate > o.OrderDate

JOIN [Order Details] od on o.OrderID = od.OrderID
join Customers c on c.CustomerID=o.CustomerID

WHERE o2.OrderDate IS NULL

So here we are joining all orders of a product with all other orders of the same product that have a greater OrderDate, and then filtering for the one that has no greater order date, so that o.OrderDate will be the MAX(OrderDate) for each ProductID

(Disclaimer: The above SQL is not tested and may require modification in order to run properly on your database, but the idea should work for your needs.)