mysql - 使用 avg 和 group by 的 SQL 查询

Question

我在为 MySQL 编写 SQL 查询时遇到了一些问题。我有一个具有以下结构的表:

mysql> select id, pass, val from data_r1 limit 10;
+------------+--------------+----------------+
| id         | pass         | val            |
+------------+--------------+----------------+
| DA02959106 | 5.0000000000 |  44.4007000000 |
| 08A5969201 | 1.0000000000 | 182.4100000000 |
| 08A5969201 | 2.0000000000 | 138.7880000000 |
| DA02882103 | 5.0000000000 |  44.7265000000 |
| DA02959106 | 1.0000000000 | 186.1470000000 |
| DA02959106 | 2.0000000000 | 148.2660000000 |
| DA02959106 | 3.0000000000 | 111.9050000000 |
| DA02959106 | 4.0000000000 |  76.1485000000 |
| DA02959106 | 5.0000000000 |  44.4007000000 |
| DA02959106 | 4.0000000000 |  76.6485000000 |

我想创建一个从表中提取以下信息的查询:

id, AVG of 'val' for 'pass' = 1, AVG of 'val' for 'pass' = 2, etc

查询的结果应该是这样的:

+------------+---------+---------+---------+---------+---------+---------+---------+
| id         | val_1   | val_2   | val_3   | val_4   | val_5   | val_6   | val_7   |
+------------+---------+---------+---------+---------+---------+---------+---------+
| DA02959106 | 186.147 | 148.266 | 111.905 | 76.3985 | 44.4007 | 0       | 0       |
+------------+---------+---------+---------+---------+---------+---------+---------+

当然，每个唯一的“id”都有更多的行。

我已经尝试了一些类似的查询

SELECT id, pass, AVG(val) AS val_1 FROM data_r1 WHERE pass = 1 GROUP BY id;

这会返回正确的结果，但我必须使用“pass”的其他可能值(最多 7 个)的结果来扩展它

我尝试在 AVG 中使用嵌套的 SELECT，但这不起作用，因为我不知道如何正确地将其限制为当前的 'id'。

然后，我创建了 View 来表示“pass”=1、“pass”=2 等的每个查询的结果。但对于大多数 id，“pass”的最大值是 5。当使用 JOIN 查询获取 View 的最终结果我收到了一个空的结果集，因为一些 View 是空的/没有特定“id”的值。

有什么想法吗？

Answer 1

如果我明白你需要什么，试试这个:

SELECT id, pass, AVG(val) AS val_1 
FROM data_r1 
GROUP BY id, pass;

或者，如果您只希望每个 ID 对应一行，则:

SELECT d1.id,
    (SELECT IFNULL(ROUND(AVG(d2.val), 4) ,0) FROM data_r1 d2 
     WHERE d2.id = d1.id AND pass = 1) as val_1,
    (SELECT IFNULL(ROUND(AVG(d2.val), 4) ,0) FROM data_r1 d2 
     WHERE d2.id = d1.id AND pass = 2) as val_2,
    (SELECT IFNULL(ROUND(AVG(d2.val), 4) ,0) FROM data_r1 d2 
     WHERE d2.id = d1.id AND pass = 3) as val_3,
    (SELECT IFNULL(ROUND(AVG(d2.val), 4) ,0) FROM data_r1 d2 
     WHERE d2.id = d1.id AND pass = 4) as val_4,
    (SELECT IFNULL(ROUND(AVG(d2.val), 4) ,0) FROM data_r1 d2 
     WHERE d2.id = d1.id AND pass = 5) as val_5,
    (SELECT IFNULL(ROUND(AVG(d2.val), 4) ,0) FROM data_r1 d2 
     WHERE d2.id = d1.id AND pass = 6) as val_6,
    (SELECT IFNULL(ROUND(AVG(d2.val), 4) ,0) FROM data_r1 d2 
     WHERE d2.id = d1.id AND pass = 7) as val_7
from data_r1 d1
GROUP BY d1.id