问题描述
考虑像这样的桌子
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,其中包含按视图计数排序的家庭 ID(例如 1、2、3 和 4)子集的前两 (2) 行.我想做类似的事情
I need to generate a result set with the top two(2) rows for a subset of family ids (say, 1,2,3 and 4) ordered by view count. I'd like to do something like
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 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,但我宁愿尽可能避免使用临时表.
but, of course, order by isn't valid in a union all context in this manner. Any suggestions? I know I could run a set of 4 queries, store the results into a temp table and select the contents of that temp as the final result, but I'd rather avoid using a temp table if possible.
注意:在实际应用中,每个family id的记录数是不确定的,view_counts也不是固定的,如上例所示.
Note: in the real app, the number of records per family id is indeterminate, and the view_counts are also not fixed as they appear in the above example.
推荐答案
你可以试试这样的
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