Linq to sql：查询句法-技术开发专区

Linq to sql：查询句法

作者：ITPUB论坛编辑： nancy 2008-01-25 00:00

where

描述：查询顾客的国家、城市和订单数信息，要求国家是法国并且订单数大于5
查询句法：

var 多条件 = from c in ctx.Customers
where c.Country == "France" && c.Orders.Count > 5
select new
{
国家 = c.Country,
城市 = c.City,
订单数 = c.Orders.Count
};

对应SQL：

SELECT [t0].[Country], [t0].[City], (
SELECT COUNT(*)
FROM [dbo].[Orders] AS [t2]
WHERE [t2].[CustomerID] = [t0].[CustomerID]
) AS [value]
FROM [dbo].[Customers] AS [t0]
WHERE ([t0].[Country] = @p0) AND (((
SELECT COUNT(*)
FROM [dbo].[Orders] AS [t1]
WHERE [t1].[CustomerID] = [t0].[CustomerID]
)) > @p1)
-- @p0: Input String (Size = 6; Prec = 0; Scale = 0) [France]

-- @p1: Input Int32 (Size = 0; Prec = 0; Scale = 0) [5]

orderby

描述：查询所有没有下属雇员的雇用年和名，按照雇用年倒序，按照名正序
查询句法：

var 排序 = from emp in ctx.Employees
where emp.Employees.Count == 0
orderby emp.HireDate.Value.Year descending, emp.FirstName ascending
select new
{
雇用年 = emp.HireDate.Value.Year,
名 = emp.FirstName
};

对应SQL：

SELECT DATEPART(Year, [t0].[HireDate]) AS [value], [t0].[FirstName]
FROM [dbo].[Employees] AS [t0]
WHERE ((
SELECT COUNT(*)
FROM [dbo].[Employees] AS [t1]
WHERE [t1].[ReportsTo] = [t0].[EmployeeID]
)) = @p0
ORDER BY DATEPART(Year, [t0].[HireDate]) DESC, [t0].[FirstName]
-- @p0: Input Int32 (Size = 0; Prec = 0; Scale = 0) [0]

分页

描述：按照每页10条记录，查询第二页的顾客
查询句法：

var 分页 = (from c in ctx.Customers select c).Skip(10).Take(10);

对应SQL：

SELECT TOP 10 [t1].[CustomerID], [t1].[CompanyName], [t1].[ContactName], [t1].[ContactTitle], [t1].[Address], [t1].[City], [t1].[Region], [t1].[PostalCode], [t1].[Country], [t1].[Phone], [t1].[Fax]
FROM (
SELECT ROW_NUMBER() OVER (ORDER BY [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax]) AS [ROW_NUMBER], [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax]
FROM [dbo].[Customers] AS [t0]
) AS [t1]
WHERE [t1].[ROW_NUMBER] > @p0
-- @p0: Input Int32 (Size = 0; Prec = 0; Scale = 0) [10]

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