03Linqtosql--查询语法.doc

03 Linq to sql--查询语法 知识点 select 描述：查询顾客的公司名、地址信息 查询句法： var 构建匿名类型1 = from c in ctx.Customers select new { 公司名 = c.CompanyName, 地址 = c.Address }; 对应SQL： SELECT [t0].[CompanyName], [t0].[Address] FROM [dbo].[Customers] AS [t0] 描述：查询职员的姓名和雇用年份 查询句法： var 构建匿名类型2 = from emp in ctx.Employees select new { 姓名 = emp.LastName + emp.FirstName, 雇用年 = emp.HireDate.Value.Year }; 对应SQL： SELECT [t0].[LastName] + [t0].[FirstName] AS [value], DATEPART(Year, [t0].[HireDate]) AS [value2] FROM [dbo].[Employees] AS [t0] 描述：查询顾客的ID以及联系信息（职位和联系人） 查询句法： var 构建匿名类型3 = from c in ctx.Customers select new { ID = c.CustomerID, 联系信息 = new { 职位 = c.ContactTitle, 联系人 = c.ContactName } }; 对应SQL： SELECT [t0].[CustomerID], [t0].[ContactTitle], [t0].[ContactName] FROM [dbo].[Customers] AS [t0] 描述：查询订单号和订单是否超重的信息 查询句法： var select带条件 = from o in ctx.Orders select new { 订单号 = o.OrderID, 是否超重 = o.Freight 100 ? 是 : 否 }; 对应SQL： SELECT [t0].[OrderID], (CASE WHEN [t0].[Freight] @p0 THEN @p1 ELSE @p2 END) AS [value] FROM [dbo].[Orders] AS [t0] -- @p0: Input Currency (Size = 0; Prec = 19; Scale = 4) [100] -- @p1: Input String (Size = 1; Prec = 0; Scale = 0) [是] -- @p2: Input String (Size = 1; Prec = 0; Scale = 0) [否] 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