选择多个记录按主键分组，并在列上具有最大值

Question

I have a table with the following structure (dummy column names and data):

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

My primary key contains columns a, b, c, d and issue.

I need a statement that first filters / groups by columns a, b, c and d and then only selects the record with MAX(issue). For this example the result set should look like this:

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

I know how I would do this for one specific record, but I cannot figure out how to do it for all the records:

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

I am using Microsoft SQL Server 2008 R2.

// Edit: Thank you guys, I found this (very compact) solution in another topic :

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

Try this:

;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

That row_number() does your ranking for you over groups defined by unique combinations of a,b,c and d.

Demo

Answer 2

Isn't this just a plain group by?

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

If contents also is required:

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)

Will list both rows if it's a tie!