Linq语句的使用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.Linq.SqlClient;

namespace _15Linq
{
    class Program
    {
        static void Main(string[] args)
        {

            //int a = 10;
            //var y = a < 10 ? a = 0 : ++a;




            //Console.WriteLine(y);

            //Console.Read();

            //新增学生
            List<Student> studentList = new List<Student>
            {
                new Student {Sno="108",Sname="曾华",Ssex="男",Sbirthday=DateTime.Parse("1977/09/01"),Class="95033" },
                new Student {Sno="105",Sname="匡明",Ssex="男",Sbirthday=DateTime.Parse("1916/10/2"),Class="95031" },
                new Student {Sno="107",Sname="王丽",Ssex="女",Sbirthday=DateTime.Parse("1976/1/23"),Class="95033" },
                new Student {Sno="101",Sname="李军",Ssex="男",Sbirthday=DateTime.Parse("1976/2/20"),Class="95033" },
                new Student {Sno="109",Sname="王芳",Ssex="女",Sbirthday=DateTime.Parse("1975/2/10"),Class="95031" },
                new Student {Sno="103",Sname="陆君",Ssex="男",Sbirthday=DateTime.Parse("1974/6/3"),Class="95031" }
            };

            //新增教师
            List<Teacher> teacherList = new List<Teacher>
            {
                new Teacher {Tno="804",Tname="李诚",Tsex="男",Tbirthday=DateTime.Parse("1958-12-02"),Prof="副教授",Depart="计算机系" },
                new Teacher {Tno="856",Tname="张旭",Tsex="男",Tbirthday=DateTime.Parse("1969-03-12"),Prof="讲师",Depart="电子工程系" },
                new Teacher {Tno="825",Tname="王萍",Tsex="女",Tbirthday=DateTime.Parse("1972-05-05"),Prof="助教",Depart="计算机系" },
                new Teacher {Tno="831",Tname="刘冰",Tsex="女",Tbirthday=DateTime.Parse("1977-08-14"),Prof="助教",Depart="电子工程系" },
            };

            //新增课程
            List<Course> courseList = new List<Course>
            {
                new Course {Cno="3-105",Cname="计算机导论",Tno="825" },
                new Course {Cno="3-245",Cname="操作系统",Tno="804" },
                new Course {Cno="6-166",Cname="数字电路",Tno="856" },
                new Course {Cno="9-888",Cname="高等数学",Tno="831" },
            };

            //新增成绩
            List<Score> scoreList = new List<Score>
            {
                new Score {Sno="103",Cno="3-245",Degree=86 },
                new Score {Sno="105",Cno="3-245",Degree=75 },
                new Score {Sno="109",Cno="3-245",Degree=68 },
                new Score {Sno="103",Cno="3-105",Degree=92 },
                new Score {Sno="105",Cno="3-105",Degree=88 },
                new Score {Sno="109",Cno="3-105",Degree=76 },
                new Score {Sno="101",Cno="3-105",Degree=64 },
                new Score {Sno="107",Cno="3-105",Degree=91 },
                new Score {Sno="108",Cno="3-105",Degree=78 },   //变换
                new Score {Sno="101",Cno="6-166",Degree=85 },
                new Score {Sno="107",Cno="6-166",Degree=79 },
                new Score {Sno="108",Cno="6-166",Degree=81 },
                //new Score {Sno="108",Cno="3-105",Degree=92 }
            };

            Console.WriteLine("1.--------【查询全部列】查询Student表中的所有记录 --------");
            var student = from s in studentList
                          select s;
            Console.WriteLine(student);
            var query1 = from s in studentList
                         select s;
            foreach(var s in query1)
            {
                Console.WriteLine("Sno:{0},Sname:{1},Ssex:{2},Class:{3}", s.Sno, s.Sname, s.Ssex, s.Class);
            }


            //匿名类型是C#3.0中新特性。其实质是编译器根据我们自定义自动产生一个匿名的类来帮助我们实现临时变量的储存。
            //匿名类型还依赖于另外一个特性：支持根据property来创建对象
            Console.WriteLine("");
            Console.WriteLine("2.--------【查询指定列】询Student表中的所有记录的Sname、Ssex和Class列--------");

            var query2 = from u in studentList
                         select new { u.Sname, u.Ssex, u.Class };
            foreach (var s in query2)
            {
                Console.WriteLine("Sname:{0},Ssex:{1},Class:{2}",s.Sname, s.Ssex, s.Class);
            }


            //SqlMethods.DateDiffYear函数是属于命名空间System.Data.Linq.SqlClient,需要引用类库：System.Data.Linq;
            Console.WriteLine("");
            Console.WriteLine("3.--------【日期函数】查询Student表中的所有记录的Sname、Ssex和Class列和年龄(通过日期函数计算得到)--------");
            var query3 = from s in studentList
                         select new { s.Sname, s.Ssex, s.Class, Age = SqlMethods.DateDiffYear(s.Sbirthday, DateTime.Now) };

            foreach(var s in query3)
            {
                Console.WriteLine("Sname:{0},Ssex:{1},Class:{2} Age:{3}", s.Sname, s.Ssex, s.Class,s.Age);
            }


            Console.WriteLine("");
            Console.WriteLine("4.--------【匿名类型中引入表达式】查询Student表中的所有记录的Sname、Ssex和Class列和年龄(通过日期函数计算得到),寿命状态(<80:短命，>=80:高寿)--------");
            var query4 = from s in studentList
                         select new { s.Sname, s.Ssex, s.Class, Age = SqlMethods.DateDiffYear(s.Sbirthday, DateTime.Now), lifetime = SqlMethods.DateDiffYear(s.Sbirthday, DateTime.Now) >= 80 ? "高寿" : "短命" };

            foreach (var s in query4)
            {
                Console.WriteLine("Sname:{0},Ssex:{1},Class:{2} Age:{3} lifetime:{4}", s.Sname, s.Ssex, s.Class, s.Age,s.lifetime);
            }

            Console.WriteLine("");
            Console.WriteLine("5.--------【去掉重复项】查询教师所有的单位即不重复的Depart列--------");

            var query5 = (from s in teacherList
                          select s.Depart).Distinct();

            foreach(var s in query5)
            {
                Console.WriteLine("Depart:{0}", s);
            }


            Console.WriteLine("");
            Console.WriteLine("6.--------【去掉重复项】查询教师所有的单位和职称(都相同的去掉)--------");
            var query6 = (from s in teacherList
                          select new { s.Depart, s.Prof }).Distinct();
            foreach (var s in query6)
            {
                Console.WriteLine("Depart:{0} Prof:{1}", s.Depart,s.Prof);
            }

            Console.WriteLine("");
            Console.WriteLine("7.--------【条件查询-关系运算与逻辑运算】查询Score表中成绩在80到100之间的所有记录--------");
            var query7 = from s in scoreList
                         where s.Degree <= 100 && s.Degree >= 80
                         select s;
            foreach(var s in query7)
            {
                Console.WriteLine("Sno:{0},Cno:{1},Degree:{2}", s.Sno, s.Cno, s.Degree);
            }


            Console.WriteLine("");
            Console.WriteLine("8.-------【模糊查询，字符串包含，以及字符串比较等于查询】 查询学生姓名包含王的学生信息");
            var query8 = from s in studentList
                         where s.Sname.Contains("王")
                         select s;
            foreach (var s in query8)
            {
                Console.WriteLine("Sno:{0},Sname:{1},Ssex:{2},Class:{3}", s.Sno, s.Sname, s.Ssex, s.Class);
            }


            Console.WriteLine("");
            Console.WriteLine("9.--------【条件查询-in查询】查询Score表中成绩为85，86或88的记录。--------");
            decimal[] arr = { 85,86,88};

            var query9 = from s in scoreList
                         where new decimal[] { 85, 86, 88 }.Contains(s.Degree)
                         select s;
            foreach (var s in query9)
            {
                Console.WriteLine("Sno:{0},Cno:{1},Degree:{2}", s.Sno, s.Cno, s.Degree);
            }

            Console.WriteLine("");
            Console.WriteLine("10.--------【条件查询-或查询】查询student表中95031班或性别为女的同学记录--------");
            var query10 = from s in studentList
                          where s.Class.Equals("95031") || s.Ssex.Equals("女")
                          select s;
            foreach (var s in query10)
            {
                Console.WriteLine("Sno:{0},Sname:{1},Ssex:{2},Class:{3}", s.Sno, s.Sname, s.Ssex, s.Class);
            }


            Console.WriteLine("");
            Console.WriteLine("");

            Console.WriteLine("11.--------【排序】以Class降序descending查询Student表的所有记录--------");

            var query11 = from s in studentList
                          orderby s.Class descending
                          select s;
            foreach (var s in query11)
            {
                Console.WriteLine("Sno:{0},Sname:{1},Ssex:{2},Class:{3}", s.Sno, s.Sname, s.Ssex, s.Class);
            }

            Console.WriteLine("");
            Console.WriteLine("");
            Console.WriteLine("12.--------【两个条件的排序】以Cno升序、Degree降序查询Score表的所有记录--------");

            var query12 = from s in scoreList
                          orderby s.Cno ascending, s.Degree descending
                          select s;
            foreach (var s in query12)
            {
                Console.WriteLine("Sno:{0},Cno:{1},Degree:{2}", s.Sno, s.Cno, s.Degree);
            }
            
            Console.WriteLine("");
            Console.WriteLine("");
            Console.WriteLine("13.--------【聚合函数的应用】查询 95031 班的学生人数--------");

            var query13 = (from s in studentList
                           where s.Class.Equals("95031")
                           select s).Count();

            Console.WriteLine("95031 班的学生人数:{0}", query13);
            
            Console.WriteLine("");
            Console.WriteLine("14.--------【聚合函数】查询'3-105'号课程的平均分--------");

            var query14 = (from s in scoreList
                           where s.Cno.Equals("3-105")
                           select s.Degree).Average();

            Console.WriteLine("'3-105'号课程的平均分:{0}", query14);


            Console.WriteLine("");
            Console.WriteLine("15.--------【聚合函数】在学生表中求女生占总人数的百分比--------");

            var query15 = studentList.Count(x => x.Ssex.Equals("女"))*1.0 / studentList.Count();

            Console.WriteLine("女生占总人数的百分比:{0}", query15.ToString("p2"));

            ///*
            //字符型转换 转为字符串  
            //12345.ToString("n"); //生成 12,345.00  
            //12345.ToString("C"); //生成 ￥12,345.00  
            //12345.ToString("e"); //生成 1.234500e+004  
            //12345.ToString("f4"); //生成 12345.0000  
            //12345.ToString("x"); //生成 3039 (16进制)  
            //12345.ToString("p"); //生成 1,234,500.00%  
            //*/

            Console.WriteLine("");
            Console.WriteLine("16.--------【连接查询,join】查询所有学生的Sname、Cno和Degree列--------");

            //方案一
            //var query16 = from s in studentList
            //              join sc in scoreList on s.Sno equals sc.Sno
            //              select new { s.Sname, sc.Cno, sc.Degree };

            //方案二
            var query16=from s in studentList
                         from sc in scoreList
                         where s.Sno == sc.Sno
                         select new { s.Sname, sc.Cno, sc.Degree };


            foreach(var s in query16)
            {
                Console.WriteLine("Sname:{0}, Cno:{1}, Degree:{2}", s.Sname, s.Cno, s.Degree);
            }

            Console.WriteLine("");
            Console.WriteLine("17.--------【连接查询 where连接】查询所有学生的Sname、Cname和Degree列--------");

            var query17 = from s in studentList
                          from sc in scoreList
                          from c in courseList
                          where s.Sno == sc.Sno && sc.Cno == c.Cno
                          select new { s.Sname, c.Cname, sc.Degree };

            foreach(var s in query17)
            {
                Console.WriteLine("Sname:{0}, Cname:{1}, Degree:{2}", s.Sname, s.Cname, s.Degree);
            }
            

            //let子句用于在LINQ表达式中存储子表达式的计算结果。let子句创建一个范围变量来存储结果，变量被创建后，
            //不能修改或把其他表达式的结果重新赋值给它。此范围变量可以在后续的LINQ子句中使用。
            Console.WriteLine("");
            Console.WriteLine("18.--------【聚合 函数的应用】查询Score表中的最高分的学生学号和课程号--------");

            var query18 = from s in scoreList
                          let scoreMax = (from u in scoreList
                                          select u.Degree).Max()
                          where s.Degree == scoreMax
                          select new { s.Sno, s.Cno };
            foreach(var s in query18)
            {
                Console.WriteLine("sno:{0}  cno:{1}",s.Sno,s.Cno);
            }
                         

            ////在Linq表达式中，into子句可以创建一个临时标识符，使用该标识符可以存储group、join或select子句的结果。
            Console.WriteLine("");
            Console.WriteLine("19.-------【分组查询】-查询Score表中至少有5名学生选修的并以3开头的课程的平均分数--------");
            var query19=from s in scoreList
                        where s.Cno.StartsWith("3")
                        group s by s.Cno
                        into cc
                        where cc.Count()>=5
                        select new {cno=cc.Key,avg=cc.Average(x=>x.Degree)};

            foreach(var s in query19)
            {
                Console.WriteLine("cno:{0}  avg:{1}",s.cno,s.avg);
            }            

            Console.WriteLine("");
            Console.WriteLine("20.--------【聚合函数的应用】查询最低分大于70，最高分小于90的Sno列--------");
            var query20 = from s in scoreList
                          group s by s.Sno
                              into cc
                              where cc.Min(x => x.Degree) >= 70 && cc.Max(x => x.Degree) <= 90
                              select new { Sno = cc.Key };

            foreach(var s in query20)
            {
                Console.WriteLine("sno:{0}",s.Sno);
            }

            Console.WriteLine("21.---------统计总成绩大于170的学生");
            var query21 = from s in scoreList
                          group s by s.Sno
                              into cc
                              where cc.Sum(x => x.Degree) > 170
                              select new { sno = cc.Key };

            var query22 = from s in query21
                          from st in studentList
                          where s.sno == st.Sno
                          select new { st.Sno, st.Sname, st.Class, st.Ssex };
            foreach(var s in query22)
            {
                Console.WriteLine("Sno:{0},Sname:{1},Class:{2},Ssex:{3}", s.Sno, s.Sname, s.Class, s.Ssex);
            }


            Console.Read();
        }
    }
}