选择多个记录按主键分组，并在列上具有最大值

Question

我有一个具有以下结构的表（虚拟列名和数据）：

+--+--+--+--+------+--------+
|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     |        |
+--+--+--+--+------+--------+

我的主键包含a，b，c，d和issue列。

我需要一条语句，该语句首先按a，b，c和d列过滤/分组，然后仅选择具有MAX（issue）的记录。 对于此示例，结果集应如下所示：

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

我知道如何对一条特定记录执行此操作，但是我无法弄清楚如何对所有记录执行此操作：

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。

//编辑：谢谢大家，我在另一个主题中找到了这个（非常紧凑的）解决方案：

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

尝试这个：

;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

该row_number（）在由a，b，c和d的唯一组合定义的组上为您排名。

演示

Answer 2

这不是一个简单的团体吗？

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

如果还需要内容：

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，将列出两行！