選擇多個記錄按主鍵分組，並在列上具有最大值

Question

我有一個具有以下結構的表（虛擬列名和數據）：

+--+--+--+--+------+--------+
|a |b |c |d |issue |content |
+--+--+--+--+------+--------+
|a |b |c |d |1     |        |
|a |b |c |d |2     |        |
|a |b |c |d |3     |        |
|d |e |f |g |1     |        |
|d |e |f |g |2     |        |
|e |f |g |h |1     |        |
+--+--+--+--+------+--------+

我的主鍵包含a，b，c，d和issue列。

我需要一條語句，該語句首先按a，b，c和d列過濾/分組，然后僅選擇具有MAX（issue）的記錄。 對於此示例，結果集應如下所示：

+--+--+--+--+------+--------+
|a |b |c |d |issue |content |
+--+--+--+--+------+--------+
|a |b |c |d |3     |        |
|d |e |f |g |2     |        |
|e |f |g |h |1     |        |
+--+--+--+--+------+--------+

我知道如何對一條特定記錄執行此操作，但是我無法弄清楚如何對所有記錄執行此操作：

SELECT TOP 1 * FROM Test_Max_N_Per_Group
WHERE a = 'a' AND b = 'b' AND c = 'c' AND d = 'd'
ORDER BY issue DESC

我正在使用Microsoft SQL Server 2008 R2。

//編輯：謝謝大家，我在另一個主題中找到了這個（非常緊湊的）解決方案：

SELECT t1.* FROM Test_Max_N_Per_Group t1
LEFT JOIN Test_Max_N_Per_Group t2
ON t1.a = t2.a AND t1.b = t2.b AND t1.c = t2.c AND t1.d  = t2.d AND
    t1.issue < t2.issue
WHERE t2.issue IS NULL

Answer 1

嘗試這個：

;with cte as
(select a,b,c,d, issue, row_number() over (partition by a,b,c,d order by issue desc) maxval, content
 from yourtable)

select a,b,c,d,issue,content
from cte
where maxval = 1

該row_number（）在由a，b，c和d的唯一組合定義的組上為您排名。

演示

Answer 2

這不是一個簡單的團體嗎？

SELECT a, b, c, d, MAX(issue)
FROM tablename
GROUP BY a, b, c, d

如果還需要內容：

SELECT a, b, c, d, issue, contents
FROM tablename t1
WHERE issue = (select max(issue) from tablename t2
               where t1.a = t2.a
                 and t1.b = t2.b
                 and t1.c = t2.c
                 and t1.d = t2.d)

如果是平局，將列出兩行！