內嵌選擇與LINQ

Question

我需要複製具有內選擇一個T-SQL語句，使用LINQ：

SELECT *, 
CustomerTypes.Description as CustomerType, 
(Select Min(Distinct DocumentStatistics.StatDateTime) As LastStatCheck 
From DocumentStatistics 
Where DocumentStatistics.CustomerId = Customers.CustomerId) As LastStatCheck 
FROM Customers 
INNER JOIN CustomerTypes ON Customers.CustomerTypeID = CustomerTypes.CustomerTypeID 
ORDER BY CustomerName 

以下是我能來最接近的，但它結束了全退DocumentStatistics，40,000以上。

  Dim docQuery = (From doc In data.DocumentStatistics _ 
         Select doc) 

     Dim query = From customer In data.Customers _ 
        Join docStat In docQuery _ 
        On customer.CustomerID Equals docStat.CustomerID _ 
        Select Customer = customer, LastStatCheck = _ 
         (From doc In docQuery Where customer.CustomerID = doc.CustomerID _ 
         Select doc.StatDateTime).Distinct().Min() 

我錯過了什麼？我如何複製初始SQL語句？

我可以帶VB或C＃的例子，我正在使用SQL Server數據庫。

Answer 1

您需要使用組加入函數來實現這一點，有點像在C＃中的以下內容：

var result = from customer in data.Customers 
      join docStat in data.DocumentStatistics 
        on customer.CustomerID equals docStat.CustomerID into stats 
      where stats.Count() > 0 
      select new 
      { 
       Customer = customer, 
       LastStatCheck = stats.Min(res => res.StatDateTime) 
      }; 

，並在VB.Net

Dim result = From customer In data.Customers _ 
      Group Join docStat In data.DocumentStatistics _ 
        On customer.CustomerID Equals docStat.CustomerID Into stats = Group _ 
      Where stats.Count() > 0 _ 
      Select New With _ 
      { _ 
       .Customer = customer _ 
       .LastStatCheck = stats.Min(Function(res) res.StatDateTime) _ 
      } 

Answer 2

約翰，

退房名爲Linqer（我有這個產品沒有關聯）的產品。它需要一個SQL語句並將其轉換爲LINQ。它能夠轉換幾乎所有的查詢。這對我來說非常有用。它也教會了我很多關於LINQ如何工作的知識。

蘭迪

Answer 3

你真正想要的是組加入。

C＃示例：

var query = from c in data.Customers 
      join ds in data.DocumentStatistics 
      on c.CustomerID equals ds.CustomerID into stats 
      select new 
      { 
       Customer = c, 
       LastStatCheck = stats.Min(s => s.StatDateTime) 
      }; 

Answer 4

Linqer從我原來的SQL語句中給了我以下結果：

From customer In data.Customers _ 
        Select _ 
        Customer = customer, _ 
        LastStatCheck = (CType((Aggregate lastDateChecked In _ 
        (From docStat In data.DocumentStatistics _ 
        Where docStat.CustomerID = customer.CustomerID _ 
        Select docStat) Into Min(lastDateChecked.StatDateTime)), DateTime?)) 

約Linqer樂於助人的事情是，我可以把在T-SQL語句和運行旁邊的LINQ語句的查詢。