Question

这是一种简单的交叉表查询。我很难将我的SQL知识转移到Linq，因为它很难测试（我没有让linqpad在WP7开发中正常运行）我不能轻易“玩”。

CREATE TABLE Store
(
    StoreID INT NOT NULL,
    StoreName VARCHAR(10) NOT NULL
)

INSERT INTO Store (StoreID,StoreName) VALUES (1,'Store A')
INSERT INTO Store (StoreID,StoreName) VALUES (2,'Store B')

CREATE TABLE ProductType
(
    ProductTypeID INT NOT NULL,
    ProductTypeName VARCHAR(20) NOT NULL
)

INSERT INTO ProductType (ProductTypeID,ProductTypeName) VALUES (1,'Clothing')
INSERT INTO ProductType (ProductTypeID,ProductTypeName) VALUES (2,'Food')

CREATE TABLE Product
(
    ProductID INT NOT NULL,
    ProductTypeID INT NOT NULL,
    ProductName VARCHAR(20) NOT NULL
)

INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (1,1,'Hat')
INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (2,1,'Shirt')
INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (3,1,'Pant')
INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (4,2,'Orange')
INSERT INTO Product (ProductID,ProductTypeID,ProductName) VALUES (5,2,'Apple')


CREATE TABLE Purchase
(
    PurchaseID INT NOT NULL,
    ProductID INT NOT NULL,
    StoreID INT NOT NULL,
    Quantity INT NULL,
    Amount INT NULL
)

INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (1,1,1,5,10)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (2,2,1,4,12)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (3,3,1,1,10)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (4,4,1,3,16)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (5,5,1,7,12)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (6,1,2,10,22)
INSERT INTO Purchase (PurchaseID,ProductID,StoreID,Quantity,Amount) VALUES (7,2,2,8,26)


SELECT s.StoreName
    ,SUM(CASE
        WHEN t.ProductTypeID=1 THEN Amount
        ELSE 0
    END ) as ClothingAmount
    ,SUM(CASE
        WHEN t.ProductTypeID=2 THEN Amount
        ELSE 0
    END )AS FoodQuantity
    ,SUM(CASE
        WHEN t.ProductTypeID=1 THEN Quantity
        ELSE 0
    END ) as ClothingAmount
    ,SUM(CASE
        WHEN t.ProductTypeID=2 THEN Quantity
        ELSE 0
    END )AS FoodQuantity
FROM Purchase u
INNER JOIN Product r
ON u.ProductID=r.ProductID
INNER JOIN ProductType t
ON r.ProductTypeID=t.ProductTypeID
INNER JOIN Store s
ON s.StoreID=u.StoreID
GROUP BY s.StoreName

Answer 1

以下是LINQ中SQL查询语句的1：1翻译：

from u in Purchases
join r in Products on u.ProductID equals r.ProductID
join t in ProductTypes on r.ProductTypeID equals t.ProductTypeID
join s in Stores on u.StoreID equals s.StoreID
group new {Purchase = u, Product = r, ProductType = t, Store = s} by s.StoreName into grouped
select new {
    StoreName = grouped.Key,
    ClothingAmount = grouped.Sum(entry => entry.ProductType.ProductTypeID == 1 ? entry.Purchase.Amount : 0),
    FoodAmount = grouped.Sum(entry => entry.ProductType.ProductTypeID == 2 ? entry.Purchase.Amount : 0),
    ClothingQuantity = grouped.Sum(entry => entry.ProductType.ProductTypeID == 1 ? entry.Purchase.Quantity : 0),
    FoodQuantity = grouped.Sum(entry => entry.ProductType.ProductTypeID == 2 ? entry.Purchase.Quantity : 0)
}

被翻译成以下SQL：

SELECT SUM(
    (CASE 
        WHEN [t2].[ProductTypeID] = @p0 THEN [t0].[Amount]
        ELSE @p1
     END)) AS [ClothingAmount], SUM(
    (CASE 
        WHEN [t2].[ProductTypeID] = @p2 THEN [t0].[Amount]
        ELSE @p3
     END)) AS [FoodAmount], SUM(
    (CASE 
        WHEN [t2].[ProductTypeID] = @p4 THEN [t0].[Quantity]
        ELSE @p5
     END)) AS [ClothingQuantity], SUM(
    (CASE 
        WHEN [t2].[ProductTypeID] = @p6 THEN [t0].[Quantity]
        ELSE @p7
     END)) AS [FoodQuantity], [t3].[StoreName]
FROM [Purchase] AS [t0]
INNER JOIN [Product] AS [t1] ON [t0].[ProductID] = [t1].[ProductID]
INNER JOIN [ProductType] AS [t2] ON [t1].[ProductTypeID] = [t2].[ProductTypeID]
INNER JOIN [Store] AS [t3] ON [t0].[StoreID] = [t3].[StoreID]
GROUP BY [t3].[StoreName]

但请注意，强烈建议在表上设置正确的主键和外键。一旦完成（并且模型相应地更新），相同的查询可以简化为：

from purchase in Purchases
group purchase by purchase.Store.StoreName into grouped
select new {
    StoreName = grouped.Key,
    ClothingAmount = grouped.Sum(purchase => purchase.Product.ProductTypeID == 1 ? purchase.Amount : 0),
    FoodAmount = grouped.Sum(purchase => purchase.Product.ProductTypeID == 2 ? purchase.Amount : 0),
    ClothingQuantity = grouped.Sum(purchase => purchase.Product.ProductTypeID == 1 ? purchase.Quantity : 0),
    FoodQuantity = grouped.Sum(purchase => purchase.Product.ProductTypeID == 2 ? purchase.Quantity : 0)
}

如何在Linq中编写此交叉表类型查询（提供的表和数据）

1 个答案: