Linq
1 基本语法
IEnumerable<int> scoreQuery =
from score in scores
where score > 80
select score;
2 分组
var queryGroupByAverages = from student in students
group new { student.FirstName, student.LastName }
by student.ExamScores.Average() > 75 into studentGroup
select studentGroup;
3 分组子查询
var queryGroupMax =
from student in students
group student by student.Year into studentGroup
select new
{
Level = studentGroup.Key,
HighestScore =
(from student2 in studentGroup
select student2.ExamScores.Average()).Max()
};
4 动态筛选选（在运行时动态指定谓词筛选器）
var queryNames =
from student in students
let i = student.ID.ToString()
where ids.Contains(i)
select new { student.LastName, student.ID };
