sql 2005 连接结果 [英] sql 2005 join results

问题描述

使用 Microsoft SQL Server 2005:

Using Microsoft SQL Server 2005:

我有一个表测试":

1 11 测试 1

2 11 test2

3 11 test3

4 12 测试4

有没有办法查询这个，并返回按link_id"分组的结果，并加入名称?

Is there a way to query this, and return the results grouped by "link_id", with the names joined?

EG，

SELECT link_id, name FROM test WHERE ?????????

SELECT link_id, name FROM test WHERE ???????

结果:

11 test1、test2、test3

11 test1, test2, test3

12 test4

推荐答案

黑盒方法是使用 CROSS APPLY 和 FOR XML PATH:

The blackbox way of doing this is with a CROSS APPLY and FOR XML PATH:

declare @t table (id int, link_id int, name varchar(max))
insert into @t select 1, 11, 'test1'
union all select 2, 11, 'test2'
union all select 3, 11, 'test3'
union all select 4, 12, 'test4'

select b.link_id, d.link_names
from (
    select distinct link_id
    from @t a
) b
cross apply (
    select name + ', ' as [text()]
    from @t c
    where b.link_id = c.link_id
    for xml path('')
) d (link_names)

对于每一行，一个 CROSS APPLY 执行应用的子查询.在这种情况下，子查询被调用两次，分别是 link_id 11 和 12.然后子查询滥用 FOR XML 运算符将字符串相加.

For each row, a CROSS APPLY executes the applied subquery. In this case, the subquery is called twice, for link_id 11 and 12. The subquery then abuses the FOR XML operator to add the strings together.

如果你运行查询，它会打印:

If you run the query, it will print:

11   test1, test2, test3, 
12   test4, 

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