对于 MySQL，我需要一份与平均值偏差超过 1 个标准差的行报告（以百分比表示）

Question

我正在尝试编写一个 MySQL 查询来计算与每种产品最常见的行有很大不同的行，并报告百分比差异，其中低于 100% 的价格低于该产品的平均价格，超过 100% 的价格较高。忽略与平均值小于 1 个标准差的价格。

示例数据：

_rowid	_时间戳	代码	fk_product_id	fk_po_id	成本
5952	2021-01-10 10:19:01	00805	1367	543	0.850
9403	2022-05-23 14:54:34	00805	1367	2942	0.850
41595	2022-11-23 11:20:26	00805	1367	3391	1.350
39635	2022-01-18 12:49:32	水1	344	3153	0.140
40134	2022-04-06 22:39:34	水1	344	2747	0.190
41676	2022-12-09 16:28:28	水1	344	3398	0.140
39634	2022-01-18 12:49:31	gr309203 344400	1024	3154	0.770
35634	2021-03-03 15:23:23	gr309203 344400	1024	3203	0.790
41264	2022-11-16 11:41:44	gr309203 344400	1024	3357	0.970

SELECT code, fk_product_id, cost, cost/
  (SELECT avg(cost) FROM po_line aa WHERE aa.code = code) AS percent 
FROM po_line 
WHERE (SELECT STDDEV(cost) FROM po_line ss WHERE ss.code = code)>1;

这不会返回任何行，但报告中应显示三行（每种产品各一行）。

预期结果应该是：

代码	fk_product_id	成本	百分比
00805	1367	1.350	133
水1	344	0.190	121
gr309203 344400	1024	0.970	115

Answer 1

此查询显示如何使用窗口函数来计算每个给定代码的标准差数量以及成本相对于平均成本的百分比。

SELECT code, cost, avg, std, 
  ABS(cost-avg)/std AS num_std, 
  cost*100/avg AS pct
FROM (
  SELECT code, cost,
    AVG(cost) OVER (PARTITION BY code) AS avg,
    STDDEV(cost) OVER (PARTITION BY code) AS std
  FROM po_line
) AS p;

结果：

+-----------------+-------+-----------+---------------------+--------------------+-------------+
| code            | cost  | avg       | std                 | num_std            | pct         |
+-----------------+-------+-----------+---------------------+--------------------+-------------+
| 00805           | 0.850 | 1.0166667 | 0.23570226039551592 | 0.7071069226079035 |  83.6065546 |
| 00805           | 0.850 | 1.0166667 | 0.23570226039551592 | 0.7071069226079035 |  83.6065546 |
| 00805           | 1.350 | 1.0166667 | 0.23570226039551592 | 1.4142134209517383 | 132.7868809 |
| gr309203 344400 | 0.770 | 0.8433333 |  0.0899382504215469 | 0.8153738777025533 |  91.3043514 |
| gr309203 344400 | 0.790 | 0.8433333 |  0.0899382504215469 | 0.5929990827042229 |  93.6758930 |
| gr309203 344400 | 0.970 | 0.8433333 |  0.0899382504215469 | 1.4083740722807512 | 115.0197674 |
| Water1          | 0.140 | 0.1566667 | 0.02357022603955158 | 0.7071081954001099 |  89.3616831 |
| Water1          | 0.190 | 0.1566667 | 0.02357022603955158 | 1.4142121481595331 | 121.2765699 |
| Water1          | 0.140 | 0.1566667 | 0.02357022603955158 | 0.7071081954001099 |  89.3616831 |
+-----------------+-------+-----------+---------------------+--------------------+-------------+

（请注意，窗口函数需要 MySQL 8.0）。

该查询仅向您显示计算是如何完成的。要获得您想要的结果：

SELECT code, fk_product_id, cost, ROUND(cost*100/avg) AS pct
FROM (
  SELECT code, cost, fk_product_id,
    AVG(cost) OVER (PARTITION BY code) AS avg,
    STDDEV(cost) OVER (PARTITION BY code) AS std
  FROM po_line
) AS p
WHERE ABS(cost-avg)/std > 1;

+-----------------+---------------+-------+------+
| code            | fk_product_id | cost  | pct  |
+-----------------+---------------+-------+------+
| 00805           |          1367 | 1.350 |  133 |
| gr309203 344400 |          1024 | 0.970 |  115 |
| Water1          |           344 | 0.190 |  121 |
+-----------------+---------------+-------+------+