问题描述
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:
I have some problems with writing a SQL query for MySQL. I have a table with the following structure:
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:
I want to create a query that extracts the following information from the table:
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:
The result of the query should look like this:
+------------+---------+---------+---------+---------+---------+---------+---------+
| 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.
with more rows for each unique 'id', of course.
我已经尝试了一些查询，例如
I already tried some queries like
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，但我必须使用其他可能的pass"值(最多 7 个)的结果来扩展它
This returns the correct result, but I have to expand it with results for the other possible values of 'pass' (up to 7)
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".
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'.
然后我创建了视图来表示pass"=1、pass"=2 等的每个查询的结果.但是对于大多数 id，pass"的最高值是 5.当使用 JOIN 查询来获取视图的最终结果我收到了一个空的结果集，因为一些视图是空的/没有特定id"的值.
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'.
有什么想法吗?
推荐答案
如果我明白你需要什么，试试这个:
If I understand what you need, try this:
SELECT id, pass, AVG(val) AS val_1
FROM data_r1
GROUP BY id, pass;
或者，如果您只想为每个 id 分配一行，则:
Or, if you want just one row for every id, this:
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
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