一步一步学Linq to sql（四）：查询句法
[2] 一步一步学Linq to sql（四）：查询句法
[3] 一步一步学Linq to sql（四）：查询句法
[4] 一步一步学Linq to sql（四）：查询句法
[5] 一步一步学Linq to sql（四）：查询句法
[6] 一步一步学Linq to sql（四）：查询句法
系列文章导航：
一步一步学Linq to sql（二）：DataContext与实体
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：
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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] |
