C#LINQ或for循环如何从数据库获取数据源？

我试图获得列中每个值相同的项的计数。例如，我有一个包含人员信息的表，我想让它遍历“名字”列，并在不指定特定名称的情况下计算其中有多少Joe和Mary。

您可以按列对数据进行分组

users.GroupBy(x => x.FirstName).Select(x => new
{
    FirstName = x.Key,
    Count = x.Count()
});

---

您可以按列对数据进行分组

users.GroupBy(x => x.FirstName).Select(x => new
{
    FirstName = x.Key,
    Count = x.Count()
});

---

尝试使用

GroupBy

：

public class People
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    static void Main(string[] args)
    {
        var peoples = new List<People>
        {
            new People { Id = 1, FirstName = "Bob", LastName = "Abc" },
            new People { Id = 2, FirstName = "Joe's", LastName = "Def" },
            new People { Id = 3, FirstName = "Mary's", LastName = "Ghi" },
            new People { Id = 4, FirstName = "Alice", LastName = "Jikl" },
            new People { Id = 5, FirstName = "Bob", LastName = "Mno" },
        };

        var groupedByFirstName = peoples
            .GroupBy(x => x.FirstName)
            .Select(x => new
            {
                FirstName = x.Key,
                Count = x.Count()
            });

        foreach (var people in groupedByFirstName)
        {
            Console.WriteLine($"FirstName: {people.FirstName}. Count: {people.Count}");
        }

        Console.ReadKey();
    }
}

公共阶层人士
{
公共int Id{get；set；}
公共字符串名{get；set；}
公共字符串LastName{get；set；}
静态void Main（字符串[]参数）
{
var=新列表
{
新人{Id=1，FirstName=“Bob”，LastName=“Abc”}，
新人{Id=2，FirstName=“乔的”，LastName=“Def”}，
新人{Id=3，FirstName=“玛丽的”，LastName=“Ghi”}，
新人{Id=4，FirstName=“Alice”，LastName=“Jikl”}，
新人{Id=5，FirstName=“Bob”，LastName=“Mno”}，
};
var groupedByFirstName=peoples
.GroupBy（x=>x.FirstName）
.选择（x=>new
{
FirstName=x.Key，
Count=x.Count（）
});
foreach（groupedByFirstName中的var人员）
{
WriteLine（$“FirstName:{people.FirstName}.Count:{people.Count}”）；
}
Console.ReadKey（）；
}
}

尝试使用

GroupBy

：

public class People
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    static void Main(string[] args)
    {
        var peoples = new List<People>
        {
            new People { Id = 1, FirstName = "Bob", LastName = "Abc" },
            new People { Id = 2, FirstName = "Joe's", LastName = "Def" },
            new People { Id = 3, FirstName = "Mary's", LastName = "Ghi" },
            new People { Id = 4, FirstName = "Alice", LastName = "Jikl" },
            new People { Id = 5, FirstName = "Bob", LastName = "Mno" },
        };

        var groupedByFirstName = peoples
            .GroupBy(x => x.FirstName)
            .Select(x => new
            {
                FirstName = x.Key,
                Count = x.Count()
            });

        foreach (var people in groupedByFirstName)
        {
            Console.WriteLine($"FirstName: {people.FirstName}. Count: {people.Count}");
        }

        Console.ReadKey();
    }
}

公共阶层人士
{
公共int Id{get；set；}
公共字符串名{get；set；}
公共字符串LastName{get；set；}
静态void Main（字符串[]参数）
{
var=新列表
{
新人{Id=1，FirstName=“Bob”，LastName=“Abc”}，
新人{Id=2，FirstName=“乔的”，LastName=“Def”}，
新人{Id=3，FirstName=“玛丽的”，LastName=“Ghi”}，
新人{Id=4，FirstName=“Alice”，LastName=“Jikl”}，
新人{Id=5，FirstName=“Bob”，LastName=“Mno”}，
};
var groupedByFirstName=peoples
.GroupBy（x=>x.FirstName）
.选择（x=>new
{
FirstName=x.Key，
Count=x.Count（）
});
foreach（groupedByFirstName中的var人员）
{
WriteLine（$“FirstName:{people.FirstName}.Count:{people.Count}”）；
}
Console.ReadKey（）；
}
}

这是否回答了您的问题？到目前为止你尝试了什么？这是否回答了你的问题？到目前为止你试过什么？