OrderBy/OrderByDescending: 用于排序数据。 Select: 用于投影数据。 GroupBy: 用于分组数据。 Join: 用于连接两个数据源。 ToList/ToArray: 将查询结果转换为列表或数组。 Count: 返回元素数量。 First/FirstOrDefault: 返回第一个元素。 Single/SingleOrDefault: 返回单个元素。 Aggregate: 对序列中的元素执行累积操...
SELECT [t0].[ContactName], ( SELECT COUNT(*) FROM [dbo].[Orders] AS [t1] WHERE [t0].[CustomerID] = [t1].[CustomerID] ) AS [ords], ( SELECT COUNT(*) FROM [dbo].[Employees] AS [t2] WHERE [t0].[City] = [t2].[City] ) AS [emps] FROM [dbo].[Customers] AS [t0]3.左...
[0] into g orderby g.Key select g; foreach (var g in groupQuery) { string fileName = $"testFile_{g.Key}.txt"; Console.WriteLine(g.Key); using StreamWriter sw = new StreamWriter(fileName); foreach (var item in g) { sw.WriteLine(item); // Output to console for ex...
select num; // 执行结果:result = { 2, 4 } 1. 2. 3. 4. 5. select select:用于选择返回的结果集。 示例: var numbers = new List<int> { 1, 2, 3, 4, 5 }; var result = from num in numbers select $"Number: {num}"; // 执行结果:result = { "Number: 1", "Number: 2", ...
select item2; foreach(var q in query) Console.Write("{0}",q); 1、LINQ 函数 1.1、查询结果过滤 :where() Enumerable.Where() 是LINQ 中使用最多的函数,大多数都要针对集合对象进行过滤,因此Where()在LINQ 的操作上处处可见,Where()的主要任务是负责过滤集合中的数据:其原型如下: ...
IEnumerable<int> orderingQuery = from num in numbers where num is < 3 or > 7 orderby num ascending select num; // Query #3. string[] groupingQuery = ["carrots", "cabbage", "broccoli", "beans", "barley"]; IEnumerable<IGrouping<char, string>> queryFoodGroups = from item in grouping...
select cust; 范围变量就像 foreach 循环中的迭代变量,但查询表达式中不会真正发生迭代。 当执行查询时,范围变量将充当对 customers 中每个连续的元素的引用。 由于编译器可以推断 cust 的类型,因此无需显式指定它。 可通过 let 子句引入其他范围变量。
/* 修改集合内所有医生的工资为10000且在职 *//* C#版本1 使用ForEach方法 */salaryList.Where(item=>item.occupation=="Doctor").ToList().ForEach(u=>{u.salary=10000;u.active=true;});/* C#版本2 使用All方法(需要返回true) */salaryList.Where(item=>item.occupation=="Doctor").ToList().All...
This may end up giving you just a single distinct combination of title, sourceid and itemid. Which from your requirements doesn't look like it will meet what you need. You will also notice that I am projecting each field in your select into a new type with out declaring the new key ...