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我有三个与此 SQL 语句相关的表。

项目

  • 项目记录 ID
  • 项目名称

项目_竞赛类别

  • ProjectCompetitionCategoryRecordId
  • 项目记录 ID
  • CompetitionCategoryRecordId

比赛类别

  • CompetitionCategoryRecordId
  • 比赛类别名称

我试图从我的表中检索的是ProjectRecordId, ProjectName, CompetitionCategoryName值。

但是 aProject可能会参与多个Competition Category. 我需要将信息放在一行中，并将比赛放在它自己的列中。

下面的例子

1. 1 | Project No 1 | Competition 1, Competition 2
2. 2 | Project No 2 | Competition 2, Competition 3, Competition 4
3. 3 | Project No 3 | Competition 1, Competition 4

这是我拥有的当前 SQL 语句：

DECLARE @Data VARCHAR(2000)
DECLARE @pID INT
DECLARE @pName VARCHAR(300)

SELECT 
    @pID = Project.ProjectRecordId, 
    @pName = Project.ProjectName,@Data = COALESCE(@Data + ',' + CompetitionCategoryName, CompetitionCategoryName)
FROM 
    Project_CompetitionCategory 
INNER JOIN
    CompetitionCategory ON Project_CompetitionCategory.CompetitionCategoryRecordId = CompetitionCategory.CompetitionCategoryRecordId 
INNER JOIN
    Project ON Project_CompetitionCategory.ProjectRecordId = Project.ProjectRecordId
WHERE 
    Project.ProjectRecordId = 10

SELECT 
   @pID AS 'Project Record ID',  
   @pName AS 'Project Name', 
   @Data AS Competition, 
   (SELECT COUNT(ProjectRecordId) FROM Presentation WHERE ProjectRecordId = @pID) AS 'Number of Recorded Presentations'

如果我删除

WHERE Project.ProjectRecordId = 10

然后它只获取最后一个值，CompetitionCategory然后搞砸了。

像下面的东西。

1. 15 | Project No 15 | Competition1, Competition 2, Competition 3, Competition 2, Competition 4

我已经阅读了这篇stackoverflow文章的各种答案Concatenate many rows into a single text string?

并用谷歌搜索在网站上找到解决方案，例如

  1. http://databases.aspfaq.com/general/how-do-i-concatenate-strings-from-a-column-into-a-single-row.html
  2. http://www.simple-talk.com/sql/t-sql-programming/concatenating-row-values-in-transact-sql/

但是我仍然找不到解决方案。我正在使用 SQL Server 2008 R2。我是 SQL 新手，想了解为什么无法获得我想要的数据。

提前致谢。

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1 回答 1

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您拥有的表结构没有很好地设计用于查询类似的东西。除了与查询连接之外，还有什么理由不能使用一对多关系结果，如下所示：

SELECT p.ProjectRecordId, p.ProjectName, cc.CompetitionCategoryName FROM Project p JOIN Project_CompetitionCategory pcc on p.ProjectRecordId = pcc.ProjectRecordId JOIN CompetitionCategory cc on pcc.CompetitionCategoryRecordId = cc.CompetitionCategoryRecordId

您提到的查询将连接您选择的 projectRecordID 的表，但删除 recordId 只会列出表中所有项目的所有可能类别。

DECLARE @compCat VARCHAR(1000)

SELECT @compCat = COALESCE(@compCat + ',', '') + cc.CompetitionCategoryName 
FROM Project p JOIN Project_CompetitionCategory pcc on p.ProjectRecordId = pcc.ProjectRecordId JOIN CompetitionCategory cc on pcc.CompetitionCategoryRecordId = cc.CompetitionCategoryRecordId WHERE p.ProjectRecordId=10

此时@compCat 将只有项目 10 的竞赛类别。删除项目 10 过滤器将生成所有项目类别的列表。为了以这种方式获得连接结果，您需要使用选择 projectId 并将其传递给连接查询的游标编写 sql ......如下所示：

DECLARE @compCat VARCHAR(1000)
DECLARE projectIdSelect CURSOR FOR SELECT ProjectRecordId FROM Project

OPEN projectIdSelect
FETCH NEXT FROM projectIdSelect INTO @projectID
WHILE @@FETCH_STATUS = 0
BEGIN
    SET @compCat = ''
    SELECT @compCat = COALESCE(@compCat + ',', '') + cc.CompetitionCategoryName 
    FROM Project p JOIN Project_CompetitionCategory pcc on p.ProjectRecordId = pcc.ProjectRecordId JOIN CompetitionCategory cc on pcc.CompetitionCategoryRecordId = cc.CompetitionCategoryRecordId WHERE p.ProjectRecordId=@vars
    PRINT('Project ID: ' + @vars + ' | ' + @compCat)    
END
CLOSE projectIdSelect 
DEALLOCATE projectIdSelect
于 2012-07-30T13:54:03.590 回答