CODEWITHSUNDEEP
sqldatabaselinq-to-sql
jlp
jlp

Reputation: 10358

How to get last children records with parent record from database

I have database with two tables: Customers (Id PK, LastName) and Orders (Id PK, CustomerId FK, ProductName, Price, etc.)

I want to retrieve only customer' last orders details together with customer name. I use .NET L2SQL but I think it's SQL question more than LINQ question so I post here SQL query I tried:

SELECT [t0].[LastName], (
    SELECT [t2].[ProductName]
    FROM (
        SELECT TOP (1) [t1].[ProductName]
        FROM [Orders] AS [t1]
        WHERE [t1].[CustomerId] = [t0].[Id]
        ORDER BY [t1].[Id] DESC
        ) AS [t2]
    ) AS [ProductName], (
    SELECT [t4].[Price]
    FROM (
        SELECT TOP (1) [t3].[Price]
        FROM [Orders] AS [t3]
        WHERE [t3].[CustomerId] = [t0].[Id]
        ORDER BY [t3].[Id] DESC
        ) AS [t4]
    ) AS [Price]
FROM [Customers] AS [t0]

Problem is that Orders has more columns (30) and with each column the query gets bigger and slower because I need to add next subqueries.

Is there any better way?

Upvotes: 3

Views: 3873

Answers (1)

Quassnoi
Quassnoi

Reputation: 425331

In SQL Server 2005 and above:

SELECT  *
FROM    (
        SELECT  o.*,
                ROW_NUMBER() OVER (PARTITION BY c.id ORDER BY o.id DESC) rn
        FROM    customers c
        LEFT JOIN
                orders o
        ON      o.customerId = c.id
        ) q
WHERE   rn = 1

or this:

SELECT  *
FROM    customers c
OUTER APPLY
        (
        SELECT  TOP 1 *
        FROM    orders o
        WHERE   o.customerId = c.id
        ORDER BY
                o.id DESC
        ) o

In SQL Server 2000:

SELECT  *
FROM    customers с
LEFT JOIN
        orders o
ON      o.id = 
        (
        SELECT  TOP 1 id
        FROM    orders oi
        WHERE   oi.customerId = c.id
        ORDER BY
                oi.id DESC
        )

Upvotes: 7

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