LINQ系列:LINQ to SQL Transact-SQL函数
1. CASE WHEN ... THEN ...
var expr = from p in context.Products
select new
{
商品ID = p.ProductID,
商品名称 = p.ProductName,
是否库存 = p.UnitsInStock > ? "是" : "否"
};
SELECT
[Extent1].[ProductID] AS [ProductID],
[Extent1].[ProductName] AS [ProductName],
CASE WHEN ([Extent1].[UnitsInStock] > 0) THEN N'是' ELSE N'否' END AS [C1]
FROM [dbo].[Product] AS [Extent1]
2. Distinct
var expr = context.Products
.Select(p => p.CategoryID)
.Distinct();
SELECT
[Distinct1].[CategoryID] AS [CategoryID]
FROM ( SELECT DISTINCT
[Extent1].[CategoryID] AS [CategoryID]
FROM [dbo].[Product] AS [Extent1]
) AS [Distinct1]
3. Count
var expr = context.Products.Count();
SELECT
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
COUNT(1) AS [A1]
FROM [dbo].[Product] AS [Extent1]
) AS [GroupBy1]
var expr = context.Products
.Count(p => p.UnitPrice > 10m);
SELECT
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
COUNT(1) AS [A1]
FROM [dbo].[Product] AS [Extent1]
WHERE [Extent1].[UnitPrice] > cast(10 as decimal(18))
) AS [GroupBy1]
4. LongCount
var expr = context.Products.LongCount();
SELECT
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
COUNT_BIG(1) AS [A1]
FROM [dbo].[Product] AS [Extent1]
) AS [GroupBy1]
var expr = context.Products
.LongCount(p => p.UnitPrice > 10m);
SELECT
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
COUNT_BIG(1) AS [A1]
FROM [dbo].[Product] AS [Extent1]
WHERE [Extent1].[UnitPrice] > cast(10 as decimal(18))
) AS [GroupBy1]
5. Sum
var expr = context.Products
.Select(p=>p.UnitsInStock)
.Sum();
var expr = context.Products
.Sum(p => p.UnitsInStock);
SELECT
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
SUM([Extent1].[UnitsInStock]) AS [A1]
FROM [dbo].[Product] AS [Extent1]
) AS [GroupBy1]
6. Min
var expr = context.Products
.Min(p => p.UnitPrice);
var expr = context.Products
.Select(p => p.UnitPrice)
.Min();
SELECT
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
MIN([Extent1].[UnitPrice]) AS [A1]
FROM [dbo].[Product] AS [Extent1]
) AS [GroupBy1]
查找每个类别中单价最低的商品:
var expr = from p in context.Products
group p by p.CategoryID into g
select new
{
CategoryID = g.Key,
CheapestProducts = from p2 in g
where p2.UnitPrice == g.Min(p3 => p3.UnitPrice)
select p2
};
SELECT
[Project1].[CategoryID] AS [CategoryID],
[Project1].[C1] AS [C1],
[Project1].[ProductID] AS [ProductID],
[Project1].[CategoryID1] AS [CategoryID1],
[Project1].[ProductName] AS [ProductName],
[Project1].[UnitPrice] AS [UnitPrice],
[Project1].[UnitsInStock] AS [UnitsInStock],
[Project1].[Discontinued] AS [Discontinued]
FROM ( SELECT
[GroupBy1].[K1] AS [CategoryID],
[Extent2].[ProductID] AS [ProductID],
[Extent2].[CategoryID] AS [CategoryID1],
[Extent2].[ProductName] AS [ProductName],
[Extent2].[UnitPrice] AS [UnitPrice],
[Extent2].[UnitsInStock] AS [UnitsInStock],
[Extent2].[Discontinued] AS [Discontinued],
CASE WHEN ([Extent2].[ProductID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
FROM (SELECT
[Extent1].[CategoryID] AS [K1],
MIN([Extent1].[UnitPrice]) AS [A1]
FROM [dbo].[Product] AS [Extent1]
GROUP BY [Extent1].[CategoryID] ) AS [GroupBy1]
LEFT OUTER JOIN [dbo].[Product] AS [Extent2] ON ([GroupBy1].[K1] = [Extent2].[CategoryID]) AND ([Extent2].[UnitPrice] = [GroupBy1].[A1])
) AS [Project1]
ORDER BY [Project1].[CategoryID] ASC, [Project1].[C1] ASC
7. Max
var expr = context.Products
.Max(p => p.UnitPrice);
var expr = context.Products
.Select(p => p.UnitPrice)
.Max();
SELECT
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
MAX([Extent1].[UnitPrice]) AS [A1]
FROM [dbo].[Product] AS [Extent1]
) AS [GroupBy1]
8.Avg
var expr = context.Products
.Select(p => p.UnitPrice)
.Average();
var expr = context.Products
.Average(p => p.UnitPrice);
SELECT
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
AVG([Extent1].[UnitPrice]) AS [A1]
FROM [dbo].[Product] AS [Extent1]
) AS [GroupBy1]
查找单个类别中单价高于平均价的产品:
var expr = from p in context.Products
group p by p.CategoryID into g
select new
{
CategoryID = g.Key,
ExpensiveProducts = from p2 in g
where p2.UnitPrice > g.Average(p3 => p3.UnitPrice)
select p2
};
SELECT
[Project1].[CategoryID] AS [CategoryID],
[Project1].[C1] AS [C1],
[Project1].[ProductID] AS [ProductID],
[Project1].[CategoryID1] AS [CategoryID1],
[Project1].[ProductName] AS [ProductName],
[Project1].[UnitPrice] AS [UnitPrice],
[Project1].[UnitsInStock] AS [UnitsInStock],
[Project1].[Discontinued] AS [Discontinued]
FROM ( SELECT
[GroupBy1].[K1] AS [CategoryID],
[Extent2].[ProductID] AS [ProductID],
[Extent2].[CategoryID] AS [CategoryID1],
[Extent2].[ProductName] AS [ProductName],
[Extent2].[UnitPrice] AS [UnitPrice],
[Extent2].[UnitsInStock] AS [UnitsInStock],
[Extent2].[Discontinued] AS [Discontinued],
CASE WHEN ([Extent2].[ProductID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1]
FROM (SELECT
[Extent1].[CategoryID] AS [K1],
AVG([Extent1].[UnitPrice]) AS [A1]
FROM [dbo].[Product] AS [Extent1]
GROUP BY [Extent1].[CategoryID] ) AS [GroupBy1]
LEFT OUTER JOIN [dbo].[Product] AS [Extent2] ON ([GroupBy1].[K1] = [Extent2].[CategoryID]) AND ([Extent2].[UnitPrice] > [GroupBy1].[A1])
) AS [Project1]
ORDER BY [Project1].[CategoryID] ASC, [Project1].[C1] ASC
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