聯盟和ORDER BY

Question

考慮像

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 

表我需要生成與前兩名（2）行設置家庭ID的子集的結果（比如，1,2,3和4）按查看次數排序。 我想這樣做

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，當然，爲了通過是無效的工會所有以該方式上下文。有什麼建議麼？我知道我可以運行一組4個查詢，存儲結果到一個臨時表，並選擇溫度作爲最終結果的內容，但我寧願避免使用臨時表如果可能的話。

注：在真正的應用程序，每個家庭的ID記錄數是不確定的，並且view_counts，因爲它們出現在上面的例子也並不固定。

Answer 1

你可以嘗試這樣的事情

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 2

用途：

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 ... 

的理由是分配一個排名，然後在此基礎上進行過濾。

Answer 3

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) 

如果你沒有一個實際的family表，您可以使用一組工會或者遞歸CTE構建它：

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) 

確保您在tbl_ranks (family_id, viewcount)有一個索引。

這將是有效的，如果你有大量的每個家庭行列的，因爲如果與PARTITION BY使用像ROW_NUMBER解析功能將無法使用TOP方法。

Answer 4

如果您使用SQL Server 2005或更高版本，可以利用分析功能優勢：

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

Answer 5

你只需要調整您建議SQL命令有點讓它像你想要的那樣工作。要綁定TOP和ORDER BY你可以把裏面你從選擇paranthesis的發言，並給出一個名稱（這裏沒有使用，但需要）。

與Adriaan Stander's answer的聲明和INSERT語句下面

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 

給

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