Question

SELECT Parent, Child FROM Daycare_Contacts
GROUP BY Parent, Child;

返回类似

的结果集

Parent     Child
Bob        Brett
Bob        Cindy
Bob        John
Alice      Pierre
Alice      John

我希望将子元素作为逗号分隔列表返回，并将不同的父元素作为相邻列。像这样：

Parent     Child
Bob        Brett, Cindy, John
Alice      Pierre, John

如果可以在LINQ中完成，我也会对此持开放态度。

Answer 1

1）您可以从T-SQL返回逗号分隔的数据。

为此目标，您需要使用FOR XML命令。

您可以查看详细信息here。

请检查下一个T-SQL脚本：

DECLARE @Daycare_Contacts TABLE
(
    Parent VARCHAR(100),
    Child  VARCHAR(100)
)

INSERT INTO @Daycare_Contacts
VALUES ('Bob', 'Brett'), ('Bob', 'Cindy'), ('Bob', 'John'), ('Alice', 'Pierre'), ('Alice', 'John')

SELECT 
    Parent,
    STUFF((SELECT ', ' + Child AS 'text()' FROM @Daycare_Contacts t WHERE t.PArent = dc.Parent FOR XML PATH('')), 1, 2, '') AS Childs
FROM @Daycare_Contacts dc
GROUP BY Parent;

结果：

Parent    Childs
--------------------------
Alice     Pierre, John
Bob       Brett, Cindy, John

2）你也可以使用LINQ。

您需要使用GroupBy方法。

示例和详细信息为here。

我的小提琴：.NET Fiddle

C＃代码示例：

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

public class Program
{
    public class SomeClass
    {
        public string Parent { get; set; }
        public string Child { get; set; }
    }


    public static void Main()
    {
        var datas = new List<SomeClass>
        {
            new SomeClass{ Parent = "Bob", Child = "Brett" },
            new SomeClass{ Parent = "Bob", Child = "Cindy" },
            new SomeClass{ Parent = "Bob", Child = "John" },
            new SomeClass{ Parent = "Alice", Child = "Pierre" },
            new SomeClass{ Parent = "Alice", Child = "John" }
        };

        var groups = datas.GroupBy(n => n.Parent)
            .Select(n => new
            {
                Parent = n.Key,
                Childs = string.Join(",", n.Select(i => i.Child))
            })
            .ToList();

        var result = string.Join("\n", groups);

        Console.WriteLine(result);
    }
}

Answer 2

正如您在SQL查询中使用的那样 - 您也可以在Linq中使用GroupBy。

例如，您有一个接收数据的类，如：

public class ReceivedDataObject
{
    public string Parent { get; set; }
    public string Child { get; set; }
}

以及包含所有已接收元素的集合，例如

var receivedData = new List<ReceivedDataObject>
{
    new ReceivedDataObject { Parent = "Bob", Child = "Brett" },
    new ReceivedDataObject { Parent = "Bob", Child = "Cindy" },
    new ReceivedDataObject { Parent = "Bob", Child = "John" },
    new ReceivedDataObject { Parent = "Alice", Child = "Pierre" },
    new ReceivedDataObject { Parent = "Alice", Child = "John" }
};

现在，您可以使用GroupBy按Parent属性对收到的对象进行分组。

var groupData = receivedData.GroupBy(rd => rd.Parent);

对于结果的输出，您可以使用

foreach(var group in groupData)
{
    Console.WriteLine($"{group.Key}: {string.Join(", ", group.Select(p => p.Child))}");
}

// Output
// Bob: Brett, Cindy, John
// Alice: Pierre, John

或作为新的项目清单：

var result = new List<ReceivedDataObject>();
foreach(var group in groupData)
{
    result.Add(new ReceivedDataObject() { Parent = group.Key, Child = string.Join(", ", group.Select(p => p.Child)) } );
}

将列条目转换为单行中逗号分隔的列表，用于不同的相邻列？

2 个答案: