List之Union(),Intersect(),Except() 即并集，交集，差集运算。

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

namespace Sample2
{
class Program
{
static void Main(string[] args)
{
//List之Union(),Intersect(),Except() 即并集，交集，差集运算
IList<Student> Students1 = new List<Student>();
Students1.Add(new Student(1, false, "张三", "深圳"));
Students1.Add(new Student(2, false, "李四", "广州"));
Students1.Add(new Student(3, false, "王五", "珠海"));
Students1.Add(new Student(4, false, "赵六", "东莞"));

IList<Student> Students2 = new List<Student>();
Students2.Add(new Student(1, false, "张三", "深圳"));
Students2.Add(new Student(5, false, "李七", "广州"));
Students2.Add(new Student(6, false, "孙八", "深圳"));
Students2.Add(new Student(7, true, "赵燕", "深圳"));

//自定义比较规则
var bingji = Students1.Union(Students2, new StudentListEquality()).ToList();//并集（AB集合所有项）
var jiaoji = Students1.Intersect(Students2, new StudentListEquality()).ToList();//交集 (AB集合共同项)
var chaji = Students1.Except(Students2, new StudentListEquality()).ToList();//差集（A集合有,B没有）

Console.WriteLine("以下是并集的结果");
bingji.ForEach(x =>
{
Console.WriteLine(x.Id.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString() + " " + x.Address.ToString());

});

Console.WriteLine("以下是交集的结果");
jiaoji.ForEach(x =>
{
Console.WriteLine(x.Id.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString() + " " + x.Address.ToString());

});

Console.WriteLine("以下是差集的结果");
chaji.ForEach(x =>
{
Console.WriteLine(x.Id.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString() + " " + x.Address.ToString());

});
Console.ReadKey();
}
}

public class Student
{
public Student(int id, bool sex, String name, String address)
{
this.Id = id;
this.Sex = sex;
this.Name = name;
this.Address = address;
}
public int Id { get; set; }
public bool Sex { get; set; }
public String Name { get; set; }
public String Address { get; set; }

}

public class StudentListEquality : IEqualityComparer<Student>
{
public bool Equals(Student x, Student y)
{
return x.Id == y.Id && x.Name == y.Name && x.Address == y.Address && x.Sex == y.Sex;
}
public int GetHashCode(Student obj)
{
return (obj == null) ? 0 : obj.ToString().GetHashCode();
}
}
}

SQLServer中通过intersect,union,except和三个关键字对应交、并、差三种集合运算。

他们的对应关系可以参考下面图示



测试示例：

构造A,B两个数据集

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A:1,2,3,4  

B:1,2,5  

WITH A AS  

(SELECT '1' tno  

UNION ALL SELECT  '2' UNION ALL SELECT  '3' UNION ALL SELECT  '4'   

),  

B AS(SELECT '1' tno  

UNION ALL SELECT  '2' UNION ALL SELECT  '5')  

查询示例：

1 Union 取合集并过滤重复数据

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--1 Union 取合集并过滤重复数据  

--结果显示: 1,2,3,4,5  

SELECT * FROM A  

UNION     

SELECT * FROM B;  

2 Union all 取合集不过滤重复数据

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--2 Union all 取合集不过滤重复数据  

--结果显示:1,2,3,4,1,2,5  

SELECT * FROM A  

UNION  all  

SELECT * FROM B;  

3 Intersect 取交集(两个表中都有数据)

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--3 Intersect 取交集  

--结果显示:1,2  

SELECT * FROM A  

Intersect    

SELECT * FROM B;  

4 except 取差集(取A-B的记录)

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--4 except 取差集  

--结果显示:3,4  

SELECT * FROM A  

except    

SELECT * FROM B;