Question

嗨，我很难理解如何从数据库中获取MAX（）和SUM（）

我的数据库有3个colums id - stuff - 得分看起来像这样

ID-STUF得分

1-1-2

1-1-3

1-2-1

1-2-3

1-3-1

1-3-3

我需要做一个

MAX（得分），其中stuff = 1且id = 1

MAX（得分），其中stuff = 2且id = 1

MAX（得分），其中stuff = 3且id = 1

等

然后a SUM（得分）全部为MAX（得分）

我有数百行，我想不出一种让它发生的方法

Answer 1

为每个你需要的东西制作子查询表导数，然后将它们全部加在一起。

SELECT SUM(a.max+b.max+c.max) as total
FROM (
    (
        SELECT MAX(score) as max
        FROM tablename
        WHERE stuff = 1 AND id = 1
    ) as a,
    (
        SELECT MAX(score) as max
        FROM tablename
        WHERE stuff = 2 AND id = 1
    ) as b,
    (
        SELECT MAX(score) as max
        FROM tablename
        WHERE stuff = 3 AND id = 1
    ) as c
);

输出：

_____________
|   total   |
+-----------+
|   12345   |
+-----------+

Answer 2

尝试使用group by获取最高分数，然后对结果求和。

表中的记录

我添加了更多记录，因此max(score)对于每个stuf都不一样。

mysql> select * from stuff;
+------+------+-------+
| id   | stuf | score |
+------+------+-------+
|    1 |    1 |     2 |
|    1 |    1 |     3 |
|    1 |    2 |     1 |
|    1 |    2 |     3 |
|    1 |    3 |     1 |
|    1 |    3 |     3 |
|    1 |    3 |     4 |
|    1 |    3 |     1 |
|    1 |    2 |     5 |
|    1 |    2 |     1 |
+------+------+-------+
10 rows in set (0.00 sec)

分组

mysql> select id, max(score) as max_score from stuff group by stuf;
+------+-----------+
| id   | max_score |
+------+-----------+
|    1 |         3 |
|    1 |         5 |
|    1 |         4 |
+------+-----------+
3 rows in set (0.00 sec)

总结

mysql> select sum(max_score) from (select id, max(score) as max_score 
       from stuff group by stuf) sum_me;
+----------------+
| sum(max_score) |
+----------------+
|             12 |
+----------------+
1 row in set (0.00 sec)

一个注意事项

请注意，如果您有更多ID，则需要将查询限制为您感兴趣的ID或适当地对最后一个查询进行分组。

mysql> select id, sum(max_score) from (select id, max(score) as max_score 
       from stuff group by id, stuf) sum_me group by id;

Answer 3

你可以试试这个

    SELECT SUM(a.max) as total
    FROM (
    (
        SELECT MAX(score) as max
        FROM tablename
        GROUP BY stuf, id
    ) as a
);

mysqli SUM和MAX结果

3 个答案: