Linq to sql（四）：查询句法(二)

 

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]