Question

HIHO，我得到了下表：

+----+----+-------+----------+
| p1 | p2 | value | position |
+----+----+-------+----------+
|  1 |  5 |     0 |        1 |
|  1 |  6 |     0 |        2 |
|  1 |  7 |     0 |        3 |
|  1 |  7 |     1 |        4 |
|  1 |  8 |     1 |        5 |
+----+----+-------+----------+

由于查询需要完全符合此结果：

+----+----+-------+----------+
| p1 | p2 | value | position |
+----+----+-------+----------+
|  1 |  5 |     0 |        1 |
|  1 |  6 |     0 |        2 |
|  1 |  7 |     1 |        4 |
|  1 |  8 |     1 |        5 |
+----+----+-------+----------+

您会注意到必须对具有相同p1和p2组合的日期集进行分组，但我需要具有最高位置值的数据集。必须保证这种行为。

我尝试过类似的事情：

SELECT *
FROM table
GROUP BY p1, p2
HAVING MAX(position)

没有正确的结果。有没有人有想法？

Answer 1

http://sqlfiddle.com/#!9/499b3/3

SELECT t.*
FROM `table` t
LEFT JOIN `table` t1
ON t.p1 = t1.p1
  AND t.p2 = t1.p2
  AND t.position<t1.position
WHERE t1.p1 IS NULL

Answer 2

有几种方法可以做到这一点。这是在子查询中使用聚合的一个选项：

select t.*
from yourtable t
   join (select p1, p2, max(position) maxposition
         from yourtable
         group by p1, p2) t2 on t.p1 = t2.p1 
                            and t.p2 = t2.p2
                            and t.position = t2.maxposition

{{3}}

Answer 3

SELECT RESULT.* 
         FROM resultset RESULT 
              INNER JOIN 
              (SELECT p1,p2,value,(MAX(position)) AS position
               FROM resultset GROUP BY p1, p2) AS T2
              ON RESULT.p1=T2.p1 AND RESULT.p2= T2.p2 AND RESULT.position=T2.position

这样可以正常使用

具有保证数据集的Mysql GROUP BY

3 个答案: