C#中的选择查询相关

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace Test
 8 {
 9     class Program
10     {
11         static void Main(string[] args)
12         {
13             List<Test> listData = new List<Test>{
14                 new Test { Name = "jiangjing", Age = 18, Sex = "boy"},
15                 new Test { Name = "wenting", Age = 17, Sex = "girl"},
16                 new Test { Name = "caihong", Age = 80, Sex = "boy"},
17                 new Test { Name = "caiyun", Age = 90, Sex = "boy"}
18             };
19 
20             //string[] names = {"jiangjing", "wenting", "caihong", "test"};
21             //1.使用查询方式
22             //var res = from n in names
23             //          where n.EndsWith("g")
24             //          orderby n.Substring(n.Length-1)
25             //          select n;
26 
27             //2.使用方法方式
28             //var res = names.OrderBy(n=>n).Where(n=>n.EndsWith("g"));
29             //foreach (var name in res)
30             //    Console.WriteLine(name);
31 
32             //3.聚合函数的相关使用,分析大型数据结果
33             //var resultData = listData.Where(t=>t.Age<20).Select(t=>t.Age);
34 
35             //4.投影:在查询中新建对象
36             //var resultData = listData.Where(t => t.Sex == "boy").Select(t => new { Name = t.Name, Age = t.Age });
37             //foreach (var item in resultData)
38             //    Console.WriteLine(item);
39 
40             //5.单值选择:Distinct()函数
41             //var resultData = listData.Where(t => t.Sex == "boy").Select(t => new { Name = t.Name, Age = t.Age }).Distinct();
42             //foreach (var item in resultData)
43             //    Console.WriteLine(item);
44 
45             //6.Any和All方法
46             //bool falg1 = resultData.Any(t=>t.Name=="jiangjing");
47             //bool falg2 = resultData.All(t => t.Name == "jiangjing");
48             //Console.Write("{0} {1}", falg1, falg2);
49 
50             //7.多级排序,使用方法也行orderby,thenby...，不过写起来还没这个清晰
51             //var resultData = from t in listData
52             //                 orderby t.Age, t.Name
53             //                 select new { Name = t.Name, Age = t.Age};
54             //foreach (var item in resultData)
55             //    Console.WriteLine(item);
56 
57             //8.组合查询
58             //var resultData = from t in listData
59             //                 group t by t.Sex into tg
60             //                 select new { SumAge = tg.Sum(t => t.Age), Sex = tg.Key };
61 
62             //foreach (var item in resultData)
63             //    Console.WriteLine(item);
64 
65             //9.查询结果使用take函数或者skip函数
66 
67             //var resultData = listData.Where(t=>t.Age<20);
68 
69             //foreach (var item in resultData.Take(1))//take函数是取结果集的前n个
70             //    Console.WriteLine(item);
71 
72             //foreach (var item in resultData.Skip(1))//skip函数则是跳过结果集的前n个
73             //    Console.WriteLine(item);
74 
75             Console.ReadKey();
76         }
77     }
78 
79     class Test
80     {
81         public string Name { get; set; }
82         public int Age { get; set; }
83 
84         public string Sex { get; set; }
85 
86         public override string ToString()
87         {
88             return "名字：" + Name + "\n" + "年龄：" + Age;
89         }
90     }
91 }