多行查询结果只有一行

Question

我正在 asp.net 中开发一个学校项目，我试图得到一个查询，结果是几行（这是正确的），只在一行上显示每个“结果”的结果，事情是该项目是一个销售游戏的网页。每个游戏都有几个开发者、流派（动作、FPS 等）、格式（数字或物理）、平台（ps3、ps4 等）和其他类似的设置。我对其进行了测试，它返回了几行，正如我之前所说的，它们可以合成为具有多个列重复的值的单行。

这里是查询：

SELECT 
    dbo.Jogos.NomeJogo AS Jogo, 
    dbo.Plataforma.Plataforma,
    dbo.Jogos.disponibilidade, 
    dbo.Jogos.Preco AS Preço, 
    dbo.Jogos.Stock, 
    dbo.Desenvolvedora.NomeDesenvolvedora AS Desenvolvedora, 
    dbo.PEGI.PEGI, 
    dbo.Formato.Formato, 
    dbo.Genero.Genero, 
    dbo.Fornecedor.NomeFornecedor AS Fornecedor 
FROM dbo.Jogos 
    INNER JOIN dbo.Desenvolvedora ON dbo.Jogos.IdDesenvolvedora = dbo.Desenvolvedora.IdDesenvolvedora 
    INNER JOIN dbo.PEGI ON dbo.Jogos.IdPegi = dbo.PEGI.IdPEGI 
    INNER JOIN dbo.GeneroJogo ON dbo.Jogos.IdJogo = dbo.GeneroJogo.IdJogo 
    INNER JOIN dbo.Genero ON dbo.GeneroJogo.IdGenero = dbo.Genero.IdGenero 
    INNER JOIN dbo.JogosFormato ON dbo.Jogos.IdJogo = dbo.JogosFormato.IdJogo 
    INNER JOIN dbo.Formato ON dbo.JogosFormato.IdFormato = dbo.Formato.IdFormato 
    INNER JOIN dbo.JogosFornecedor ON dbo.Jogos.IdJogo = dbo.JogosFornecedor.IdJogo 
    INNER JOIN dbo.Fornecedor ON dbo.JogosFornecedor.IdFornecedor = dbo.Fornecedor.IdFornecedor 
    INNER JOIN dbo.JogosPlataforma ON dbo.Jogos.IdJogo = dbo.JogosPlataforma.IdJogo 
    INNER JOIN dbo.Plataforma ON dbo.JogosPlataforma.IdPlataforma = dbo.Plataforma.IdPlataforma

查询返回同一游戏的几行，可以恢复到只有一个。

例如：

Game              |  Genre   |  Platform  |  Developper
___________________________________________________________

Assassin's Creed  |  Action  |  Ps3       |  Ubisoft
Assassin's Creed  |  Stealth |  Ps3       |  Ubisoft
Assassin's Creed  |  Action  |  xBox 360  |  Ubisoft

我想获得类似的东西：

Game              |  Genre           |  Platform       |  Developper
_____________________________________________________________________

Assassin's Creed  |  Action, Stealth |  Ps3, Xbox 360  |  Ubisoft

我正在寻求帮助，因为我不明白这怎么可能。

任何帮助将不胜感激。

P.S.：查询中的一些值是葡萄牙语。 我也检查了这个线程 How to use GROUP BY to concatenate strings in SQL Server? 但是这个只使用一个表，我从几个表中获取数据，所以我真的不知道如何在这个表中进行。

提前谢谢你 最好的祝福， 凯文

Answer 1

有几种方法可以解决这个问题。 Lanorkin 在他/她的评论中引用的问题的公认答案显示了其中一个与 SQL Serer (XML PATH) 一起使用的问题。如果这听起来很深奥或令人恐惧，您可以使用关联子查询和用户定义的函数，为您连接值。

基本思想是，您有一个返回游戏的每个唯一值的外部查询和一个提取流派、平台或开发者的串联列表的内部查询。

create function getPlatforms (@jogoId nvarchar(50))
returns nvarchar(1024)
as 
begin
  declare @platforms nvarchar(1024);
  select @platforms = '';
  -- I understand that your Platform is normalized in your schema, but 
  -- you get the ide. Just make this a join. You can also strip out the 
  -- leading comma one you are done.
  select @platforms = @platforms + ', ' + Plataforma from dbo.Jogos 
        where JogoId = @jogoid;
  return @platforms;
end;
go;


SELECT 
    dbo.Jogos.NomeJogo AS Jogo, 
    dbo.getPlatforms(JogoId)
FROM dbo.Jogos 
GROUP BY NomeJogo, JogoId;

不幸的是，group_concat 在 SQL Server 中不可用（开箱即用），即连接不是聚合操作之一（与 SUM、COUNT、AVG 等不同）。

各种方法的比较，包括它们的执行方式，是here。

Answer 2

正如其他人所说，您可以使用 xml 路径对 concat 进行分组。但是，根据处理大型数据集的个人经验，我发现从查询中获取结果然后将它们连接到代码中要快得多。

例如，您可以这样创建一个对象：

public class Game
{
    public string Title { get; set; }
    public string Genre { get; set; }
    public string Platform { get; set; }
    public string Developer { get; set; }
}

然后，您可以使用 linq 以您认为合适的方式操作从查询返回的数据集。例如：

using(var command = new SqlCommand())
{
     /*init your sql command */
     var dataSet = new DataSet("Games");
     var dataAdapter = new SqlDataAdapter();
     /*set data adapter command (your query)*/
     dataAdapter.Fill(dataSet);

     var games = new List<Game>();

     var groupings = dataSet.Tables[0].Cast<DataRow>().GroupBy(x => x["Game"].ToString()); //Here we are grouping by games. Based on your example we'll have one group "Assassin's Creed". 

     foreach(var grouping in groupings)
     {
          var firstRow = grouping.First();

          var game = new Game()
          {
               Title = firstRow["Game"].ToString(),
               Genre = string.Join(",", grouping.GroupBy(x => x["Genre"]).Select(x => x.First()["Genre"].ToString()), //Grouping eliminates dupes. This should return Action, Stealth based on your example
               Platform = string.Join(",", grouping.GroupBy(x => x["Platform"]).Select(x => x.First()["Platform"].TosString()),
               Developer = firstRow["Developer"].ToString() //I'm assuming each game has exactly one developer
          }
          games.Add(game);
    }
    //The games list should now have exactly what you need. Based on your example it would have only looped once since there is only one game so you'll have a list with one game object
}

我不确定这是否对您有帮助，但我注意到这比在 sql server 中按 xml 路径进行分组要快得多。

Answer 3

这叫group_concat in sql server

喜欢：

CREATE TABLE #GAME ([NAME] varchar(50), [Genre] VARCHAR(50), [Platform] varchar(50),Developper VARCHAR(50))

INSERT INTO #GAME  VALUES ('A','g1','ps1','User1'),('A','g2','ps2','User2'),('A','g3','ps1','User1')


SELECT 
  [NAME],
  STUFF((SELECT ', ' + [Genre] FROM #GAME WHERE (NAME = Results.NAME) FOR XML PATH(''),TYPE).value('(./text())[1]','VARCHAR(MAX)'),1,2,'') AS GEN1,
  STUFF((SELECT ', ' + [Platform] FROM #GAME WHERE (NAME = Results.NAME) FOR XML PATH(''),TYPE).value('(./text())[1]','VARCHAR(MAX)'),1,2,'') AS Platform1,
  STUFF((SELECT ', ' + Developper FROM #GAME WHERE (NAME = Results.NAME) FOR XML PATH(''),TYPE).value('(./text())[1]','VARCHAR(MAX)'),1,2,'') AS Developper1

FROM #GAME Results
GROUP BY NAME

编辑 2：

CREATE TABLE #GAME ([NAME] varchar(50), [Genre] VARCHAR(50), [Platform] int,Developper VARCHAR(50))
INSERT INTO #GAME  VALUES ('A','g1',1,'User1'),('A','g2',2,'User2'),('A','g3',3,'User1')

Create Table #PLATFORM(ID int,NAME varchar(50),)
INSERT INTO #PLATFORM  VALUES (1,'ps1'),(2,'ps2'),(3,'ps3')


;with cte as
(select gm.Name as Name,pl.Name as plt
from #GAME gm join #PLATFORM pl on gm.Platform=pl.ID
)

select Name,
STUFF((SELECT ', ' + plt FROM cte WHERE (NAME = Results.NAME) FOR XML PATH(''),TYPE).value('(./text())[1]','VARCHAR(MAX)'),1,2,'') AS Platform1
FROM cte Results
GROUP BY NAME