Question

考虑像

这样的表格

tbl_ranks
--------------------------------
family_id | item_id | view_count 
--------------------------------
1           10        101
1           11        112
1           13        109

2           21        101
2           22        112
2           23        109

3           30        101
3           31        112
3           33        109

4           40        101
4           51        112
4           63        109

5           80        101
5           81        112
5           88        109

我需要为查看计数排序的族id（例如1,2,3和4）的子集生成前两（2）行的结果集。我想做一些像

这样的事情

select top 2 * from tbl_ranks where family_id = 1 order by view_count
union all
select top 2 * from tbl_ranks where family_id = 2 order by view_count
union all
select top 2 * from tbl_ranks where family_id = 3 order by view_count
union all
select top 2 * from tbl_ranks where family_id = 4 order by view_count

但是，当然，以为单位>以这种方式在 union all 上下文中无效。有什么建议？我知道我可以运行一组4个查询，将结果存储到临时表中并选择该临时表的内容作为最终结果，但是如果可能的话我宁愿避免使用临时表。

注意：在真实应用中，每个系列ID的记录数量是不确定的，并且view_counts也没有像上面示例中显示的那样修复。

Answer 1

使用：

SELECT *
  FROM (select *,
               ROW_NUMBER() OVER (PARTITION BY family_id ORDER BY view_count DESC) 'rank'
          from tbl_ranks) x
  WHERE x.rank <= 2
ORDER BY ...

理由是指定排名，然后根据它进行过滤。

Answer 2

SELECT  tro.*
FROM    family
CROSS APPLY
        (
        SELECT  TOP 2 *
        FROM    tbl_ranks tr
        WHERE   tr.family_id = family.id
        ORDER BY
                view_count DESC
        ) tro
WHERE   family.id IN (1, 2, 3, 4)

如果您没有实际的family表，可以使用一组联合或递归CTE构建它：

WITH   family AS
       (
       SELECT  1 AS id
       UNION ALL
       SELECT  2 AS id
       UNION ALL
       SELECT  3 AS id
       UNION ALL
       SELECT  4 AS id
       )
SELECT  tro.*
FROM    family
CROSS APPLY
        (
        SELECT  TOP 2 *
        FROM    tbl_ranks tr
        WHERE   tr.family_id = family.id
        ORDER BY
                view_count DESC
        ) tro
WHERE   family.id IN (1, 2, 3, 4)

确保您在tbl_ranks (family_id, viewcount)上有索引。

如果每个家庭有很多排名，这将会很有效，因为ROW_NUMBER等分析函数如果与TOP一起使用，则不会使用PARTITION BY方法。

Answer 3

如果您使用的是SQL Server 2005或更高版本，则可以利用分析功能：

SELECT * FROM (
   SELECT rank() OVER (PARTITION BY family_id ORDER BY view_count) AS RNK, * FROM ...
     )
WHERE RNK <= 2
ORDER BY ...

Answer 4

您可以尝试这样的事情

DECLARE @tbl_ranks TABLE(
        family_id INT,
        item_id INT,
        view_count INT
)

INSERT INTO @tbl_ranks SELECT 1,10,101
INSERT INTO @tbl_ranks SELECT 1,11,112
INSERT INTO @tbl_ranks SELECT 1,13,109

INSERT INTO @tbl_ranks SELECT 2,21,101
INSERT INTO @tbl_ranks SELECT 2,22,112
INSERT INTO @tbl_ranks SELECT 2,23,109

INSERT INTO @tbl_ranks SELECT 3,30,101
INSERT INTO @tbl_ranks SELECT 3,31,112
INSERT INTO @tbl_ranks SELECT 3,33,109

INSERT INTO @tbl_ranks SELECT 4,40,101
INSERT INTO @tbl_ranks SELECT 4,51,112
INSERT INTO @tbl_ranks SELECT 4,63,109

INSERT INTO @tbl_ranks SELECT 5,80,101
INSERT INTO @tbl_ranks SELECT 5,81,112
INSERT INTO @tbl_ranks SELECT 5,88,109

SELECT  *
FROm    (
            SELECT  *,
                    ROW_NUMBER() OVER(PARTITION BY family_id ORDER BY view_count DESC) MyOrder
            FROM    @tbl_ranks
        ) MyOrders
WHERE   MyOrder <= 2

Answer 5

您只需稍微调整建议的SQL命令，使其按您的需要运行。要绑定TOP和ORDER BY，您可以将语句放在您选择的paranthesis中并给出一个名称（此处不使用但需要）。

使用Adriaan Stander's answer中的DECLARE和INSERT语句以下

SELECT * FROM (SELECT TOP 2 * FROM @tbl_ranks WHERE family_id = 1 ORDER BY view_count) AS dummy1 UNION ALL
SELECT * FROM (SELECT TOP 2 * FROM @tbl_ranks WHERE family_id = 2 ORDER BY view_count) AS dummy2 UNION ALL
SELECT * FROM (SELECT TOP 2 * FROM @tbl_ranks WHERE family_id = 3 ORDER BY view_count) AS dummy3 UNION ALL
SELECT * FROM (SELECT TOP 2 * FROM @tbl_ranks WHERE family_id = 4 ORDER BY view_count) AS dummy4

给出

family_id   item_id view_count
1   10  101
1   13  109
2   21  101
2   23  109
3   30  101
3   33  109
4   40  101
4   63  109

联盟和秩序

5 个答案: