当我尝试加入两个具有一对多关系的表时，我遇到了类似的问题。在 SQL 2005 中，我发现该XML PATH方法可以非常轻松地处理行的连接。

如果有一个表叫STUDENTS

SubjectID       StudentName
----------      -------------
1               Mary
1               John
1               Sam
2               Alaina
2               Edward

我预期的结果是：

SubjectID       StudentName
----------      -------------
1               Mary, John, Sam
2               Alaina, Edward

我使用了以下内容T-SQL：

SELECT Main.SubjectID,
       LEFT(Main.Students,Len(Main.Students)-1) As "Students"
FROM
    (
        SELECT DISTINCT ST2.SubjectID, 
            (
                SELECT ST1.StudentName + ',' AS [text()]
                FROM dbo.Students ST1
                WHERE ST1.SubjectID = ST2.SubjectID
                ORDER BY ST1.SubjectID
                FOR XML PATH (''), TYPE
            ).value('text()[1]','nvarchar(max)') [Students]
        FROM dbo.Students ST2
    ) [Main]

如果您可以在开头连接逗号并使用substring跳过第一个逗号，那么您可以以更紧凑的方式执行相同的操作，这样您就不需要执行子查询：

SELECT DISTINCT ST2.SubjectID, 
    SUBSTRING(
        (
            SELECT ','+ST1.StudentName  AS [text()]
            FROM dbo.Students ST1
            WHERE ST1.SubjectID = ST2.SubjectID
            ORDER BY ST1.SubjectID
            FOR XML PATH (''), TYPE
        ).value('text()[1]','nvarchar(max)'), 2, 1000) [Students]
FROM dbo.Students ST2

QL Server 2017+ 和 SQL Azure：STRING_AGG

从 SQL Server 的下一个版本开始，我们终于可以跨行连接，而无需求助于任何变量或 XML 巫术。

STRING_AGG (Transact-SQL)

不分组

SELECT STRING_AGG(Name, ', ') AS Departments
FROM HumanResources.Department;

分组：

SELECT GroupName, STRING_AGG(Name, ', ') AS Departments
FROM HumanResources.Department
GROUP BY GroupName;

具有分组和子排序

SELECT GroupName, STRING_AGG(Name, ', ') WITHIN GROUP (ORDER BY Name ASC) AS Departments
FROM HumanResources.Department
GROUP BY GroupName;