2

表Master：

----------------------
| Name      | ID     |
----------------------
| A         | 1      |
| B         | 2      |
| C         | 3      |
----------------------

表Detail：

----------------------
| masterID  | det     |
----------------------
| 1         | 21      |
| 1         | 31      |
| 1         | 442     |
| 1         | 76      |
| 2         | 1       |
| 2         | 90      |
| 3         | 48      |
| 3         | 56      |
| 3         | 109     |
----------------------

要求的结果：进行连接和连接，但将连接值的数量限制为 X（此处为 2），如果更多，则创建一个新行。例如，上面的预期结果将是：

----------------------
| Name      | dets   |
----------------------
| A         | 21, 31 |
| A         | 442, 76|
| B         | 1, 90  |
| C         | 48, 56 |
| C         | 109    |
----------------------

使用下面的代码，我可以得到所有结果连接但是我需要关于如何限制连接记录数量的帮助：

SELECT Master.Name, 
STUFF((
SELECT ','+Detail.det
FROM Detail
WHERE Master.ID = Detail.masterID
FOR XML PATH(''),TYPE).value('(./text())[1]','VARCHAR(MAX)')
,1,2,'')
FROM Master

还为它创建了 SQLFiddle：http ://sqlfiddle.com/#!6/a1b69/1/0

4

2 回答 2

3

使用row_number()整数除法创建一个键，每隔一行递增一次。在 CTE 中执行此操作，并在主查询和 for xml 查询中使用 CTE。

SQL小提琴

MS SQL Server 2014 架构设置：

create table Master
(
  Name varchar(10),
  ID int
);

create table Detail
(
  masterID int,
  det varchar(10)
);

go

insert into Master values
('A', 1),
('B', 2),
('C', 3);

insert into Detail values
(1, 21 ),
(1, 31 ),
(1, 442),
(1, 76 ),
(2, 1  ),
(2, 90 ),
(3, 48 ),
(3, 56 ),
(3, 109);

查询 1：

with C as
(
  select M.Name,
         D.masterID,
         D.det,
         (row_number() over(partition by D.masterID order by D.det) - 1) / 2 as rn
  from dbo.Detail as D
    inner join dbo.Master as M
      on D.masterID = M.ID
)
select C.Name,
       stuff ((select ', ' + D.det
               from C as D
               where C.masterID = D.masterID and
                     C.rn = D.rn
               for xml path(''), type).value('text()[1]', 'varchar(max)'), 1, 2, '')
from C
group by C.masterID,
         C.Name,
         C.rn

结果：

| Name |         |
|------|---------|
|    A |  21, 31 |
|    A | 442, 76 |
|    B |   1, 90 |
|    C | 109, 48 |
|    C |      56 |
于 2015-04-20T11:46:16.270 回答
0

FOR XML适用于结果集的结构。我很确定你可以通过TOP 2在子查询中使用来做到这一点。

但是，您可能会发现条件聚合更快：

select m.name,
       (max(case when seqnum = 1 then cast(id as varchar(255)) else '' end) +
        max(case when seqnum = 2 then ', ' + cast(id as varchar(255)) else '' end) 
       ) as ids
from master m join
     (select d.*,
             row_number() over (partition by m.masterId order by (select null)) as seqnum
      from detail d
     ) d
     on m.id = d.masterid
where seqnum <= 2
group by name;

或者，因为您似乎并不关心特定的 id，所以使用 min 和 max：

select m.name,
       (case when minid = maxid then cast(minid as varchar(255))
             else cast(minid as varchar(255)) + ', ' + cast(maxid as varchar(255))
        end) as ids
from master m join
     (select d.masterid, min(id) as minid, max(id) as maxid
      from detail d
      group by d.masterid
     ) d
     on m.id = d.masterid;
于 2015-04-20T11:09:40.807 回答