Linq to sql（四）：查询句法(一)

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]