MySQL 带有 avg 和 group by 的 SQL 查询
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SQL query with avg and group by
提问by theFen
I have some problems with writing a SQL query for MySQL. I have a table with the following structure:
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 |
I want to create a query that extracts the following information from the table:
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
The result of the query should look like this:
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 |
+------------+---------+---------+---------+---------+---------+---------+---------+
with more rows for each unique 'id', of course.
当然，每个唯一的“id”都有更多行。
I already tried some queries like
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;
This returns the correct result, but I have to expand it with results for the other possible values of 'pass' (up to 7)
这将返回正确的结果，但我必须使用其他可能的“pass”值（最多 7）的结果来扩展它
I tried to use a nested SELECT within AVG but this didn't work because I didn't figure out how to correctly limit it to the current 'id'.
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它限制为当前的“id”。
I then created Views to represent the result of each query for 'pass' = 1, 'pass' = 2, etc. But for most ids the highest value for 'pass' is 5. When using JOIN queries to get the final result from the views I received an empty result set, because some of the Views are empty / don't have values for a specific 'id'.
然后我创建了视图来表示每个查询的结果，如 'pass' = 1、'pass' = 2 等。但对于大多数 id，'pass' 的最高值为 5。当使用 JOIN 查询获取最终结果时我收到一个空结果集的视图，因为某些视图是空的/没有特定“id”的值。
Any ideas?
有任何想法吗？
回答by Marco
If I understand what you need, try this:
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;
Or, if you want just one row for every id, this:
或者，如果您只想为每个 id 分配一行，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
回答by Cristian Iordache
As I understand, you want the average value for each id at each pass. The solution is
据我了解，您希望每次通过时每个 id 的平均值。解决办法是
SELECT id, pass, avg(value) FROM data_r1
GROUP BY id, pass;
