Question

我有以下SQL查询来返回没有分配零件的OrderLines的所有客户 - 即我只希望每个订单的每个订单行没有分配零件的客户 - （在实际问题我正在处理不同的域，但已转换为客户/订单以说明问题）

SELECT c.Customer_PK
FROM Customers c
  INNER JOIN Orders o
  ON c.Customer_PK = o.Customer_FK
  LEFT OUTER JOIN OrderLines l
  ON o.Order_PK = l.Order_FK
  LEFT OUTER JOIN Parts p
  ON l.OrderLine_PK = p.OrderLine_FK
GROUP BY c.Customer_PK
HAVING COUNT(p.Part_PK) = 0

我在LINQ中提出的最好成绩如下：

Dim qry =     
(From c In context.Customers
 Select New With { c.Customer_PK,
                  .CountParts = 
                      (From o In c.Orders
           From l In o.OrderLines
                       Select l.Parts.Count).DefaultIfEmpty.Sum})

qry = (From grp In qry
       Where grp.CountParts  = 0
       Select grp.Customer_PK)

这可行，但生成的SQL不是最佳的 - 它在客户查询的每一行上为Count执行子查询，而不是使用Group By和Having。我尝试使LINQ Group By语法工作，但它继续将过滤器作为WHERE而不是HAVING子句。

有什么想法吗？

编辑以回复以下答案：

我接受JamieSee的回答，因为它解决了陈述的问题，即使它没有产生我最初拥有的GROUP BY HAVING查询。

感谢Peter和Nick对此的意见。我是一个VB开发人员，所以我有一个破解将你的代码转换为VB，这是我最接近但它不能产生所需的输出：

Dim qry = From c In context.Customers
          Group Join o In context.Orders On c.Customer_PK Equals o.Customer_FK
          Into joinedOrders = Group
          From jo In joinedOrders.DefaultIfEmpty
          Group Join l In context.OrderLines On jo.Order_PK Equals l.Order_FK
          Into joinedLines = Group
          From jl In joinedLines.DefaultIfEmpty
          Group c By Key = New With {c.Customer_PK, jl} Into grp = Group
          Where Key.jl Is Nothing OrElse Not Key.jl.Parts.Any
          Select c.Customer_PK

我遇到的问题是我必须将“jl”推入Group By“Key”，以便我可以从Where子句中引用它，否则编译器无法看到该变量或该组之前出现的任何其他变量按条款。

根据指定的过滤器，我得到所有客户，其中至少有一个订单的行没有任何部分，而不是只有没有任何部件的客户。

Answer 1

鉴于您不关心计数，只考虑最终客户，请考虑以下重述问题：

识别所有没有任何订单行的客户。

这会产生：

var customersWithoutParts = from c in Context.Customers
                            where !(from o in Context.Orders
                                    from l in o.Lines
                                    from p in l.Parts
                                    select o.Customer_FK).Contains(c.Customer_PK)
                            select c.Customer_PK;

这应该产生的SQL大致相当于以下内容：

SELECT     c.Customer_PK
FROM         Customers AS c
WHERE     (NOT EXISTS
                          (SELECT     o.Cusomer_FK
                            FROM          Orders AS o INNER JOIN
                                                   OrderLines AS l ON o.Order_PK = l.Order_FK INNER JOIN
                                                   Parts AS p ON l.OrderLine_PK = p.OrderLine_FK
                            WHERE      (o.Customer_FK = c.Customer_PK)))

要获得您尝试重现的SQL，我首先尝试以下方法：

var customersWithoutParts = from c in Context.Customers
                            from o in c.Orders.DefaultIfEmpty()
                            from l in o.Lines.DefaultIfEmpty()
                            join part in Context.Parts on part.OrderLine_FK equals l.OrderLine_PK into joinedParts
                            where joinedParts.Count() == 0
                            select c.Customer_PK;

请注意，在VB中，此处的join将替换为Group Join。

Answer 2

在没有生成的modlls（C＃）的情况下，很难创建一个查询：

from o in dc.Orders
join jOrderLines in dc.OrderLines on o.Order_PK equals jOrderLines.Order_FK into joinedOrderlines
from l in joinedOrderLines.DefaultIfEmpty() 
group o by o.Customer_FK into g
where l == null || l.Count(x => x.Parts) == 0
select g.Key

Answer 3

这样的事情：

var qry = from c in db.Customers
            join o in db.Orders.Where(x => x.Customer_FK == c.Customer_PK)
            join l in db.OrderLines.Where(x => x.Order_FK = o.Order_PK).DefaultIfEmpty()
            join p in db.Parts.Where(x => x.OrderLine_FK = l.OrderLine_PK).DefaultIfEmpty()
            group c by new
            {
                c.Customer_PK
            } into g
            where g.Count(p => p.Part_PK != null) == 0
            select new
            {
                Customer_PK = g.Key.Customer_PK
            };

Group By拥有和计数为具有乘法嵌套表的LINQ查询

3 个答案: