sql - 联合和排序依据

Question

考虑一个像这样的表

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

我需要生成一个结果集，其中包含按观看次数排序的家庭 ID 子集(例如 1、2、3 和 4)的前两 (2) 行。我想做类似的事情

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，order by 在这种方式的 union all 上下文中是无效的。有什么建议么？我知道我可以运行一组 4 个查询，将结果存储到临时表中，然后选择该临时表的内容作为最终结果，但如果可能的话，我宁愿避免使用临时表。

注意:在实际应用中，每个家庭 ID 的记录数是不确定的，并且 view_counts 也不像上面示例中那样固定。

Answer 1

你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