sql - 将重复记录合并到 1 个字段中

Question

我有一个包含联系人列表的数据库表，其中一些联系人可能有多个记录，例如

CustomerID, CustomerName, Vehicle
1, Dan, Mazda
1, Dan, Suzuki
2, John, Ford
3, Dasha, Volvo
3, Dasha, Ford

我可以编写一个选择查询来返回不同的 customerID 和 CustomerName，以及 1 条记录中的车辆列表吗？即

1, Dan, Mazda+Suzuki
2, John, Ford
3, Dasha, Volvo+Ford

谢谢

Answer 1

有一些nice answers to this problem on another question 。

根据the linked article ，由于使用了 XML 函数，这仅适用于 SQL Server 2005 及以上版本。摘自文章-

SELECT table_name, 
       LEFT(column_names,LEN(column_names) - 1)   AS column_names 
FROM   (SELECT table_name, 
               (SELECT column_name + ',' AS [text()] 
                FROM   information_schema.columns AS internal 
                WHERE  internal.table_name = table_names.table_name 
                FOR xml PATH ('') 
               ) AS column_names 
        FROM   (SELECT   table_name 
                FROM     information_schema.columns 
                GROUP BY table_name) AS table_names) AS pre_trimmed;

Second version (admittedly inspired by this post, which I stumbled on after writing the first version):

SELECT table_name, 
       LEFT(column_names,LEN(column_names) - 1)   AS column_names 
FROM   information_schema.columns AS extern 
       CROSS APPLY (SELECT column_name + ',' 
                    FROM   information_schema.columns AS intern 
                    WHERE  extern.table_name = intern.table_name 
                    FOR XML PATH('') 
                   ) pre_trimmed (column_names) 
GROUP BY table_name,column_names;

The second CROSS APPLY version is supposedly slower according to the execution plan, but I didn’t conduct any benchmarks at all.