使用avg和分组依据的SQL查询

Question

我在为MySQL编写SQL查询时遇到一些问题。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 |

我想创建一个查询，该查询从表中提取以下信息：

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

查询结果应如下所示：

+------------+---------+---------+---------+---------+---------+---------+---------+
| 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”具有更多行。

我已经尝试过一些查询，例如

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

这将返回正确的结果，但是我必须使用“ pass”的其他可能值（最多7个）来扩展它

我尝试在AVG中使用嵌套的SELECT，但这没有用，因为我没有弄清楚如何正确地将其限制为当前的’id’。

然后，我创建了Views来表示每个查询的结果，其中“ pass” = 1，“ pass” = 2等。但是对于大多数id，“
pass”的最大值是5。当使用JOIN查询从中获取最终结果时这些视图收到的结果集为空，因为某些视图为空/没有特定“ id”的值。

有任何想法吗？

Answer 1

如果我了解您的需求，请尝试以下操作：

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

或者，如果每个ID只需要一行，则可以执行以下操作：

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