SQL到LINQ等效

        var salaries = persons
            .Where(p => p.DeptId == 1 || p.DeptId == 2)
            .GroupBy(p => p.DeptId)
            .Select(x => new { DeptId = x.Key, TotalSalary = x.Sum(p => p.Salary)});

下面是一个完整的例子:

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    class Person
    {
        public int DeptId { get; set; }
        public int Salary { get; set; }
    }

    static void Main(string[] args)
    {
        List<Person> persons = new List<Person>();
        persons.Add(new Person { DeptId = 1, Salary = 10000 });
        persons.Add(new Person { DeptId = 1, Salary = 20000 });
        persons.Add(new Person { DeptId = 1, Salary = 30000 });
        persons.Add(new Person { DeptId = 2, Salary = 40000 });
        persons.Add(new Person { DeptId = 3, Salary = 50000 });

        var salaries = persons
            .Where(p => p.DeptId == 1 || p.DeptId == 2)
            .GroupBy(p => p.DeptId)
            .Select(x => new { DeptId = x.Key, TotalSalary = x.Sum(p => p.Salary)});

        foreach (var dept in salaries)
            Console.WriteLine("{0}: {1}", dept.DeptId, dept.TotalSalary);
    }
}

输出:

1: 60000
2: 40000

var qry = from p in dc.Persons
where p.deptid==1 || p.deptid==2
group p by p.deptid into g
select new { Total = g.Sum(q=>q.salary), DeptId=g.Key };