找到有效验证之间的标准偏差天数

Question

我必须计算

1. 有效验证之间的平均天数
2. 有效验证之间的天数标准差

例如我有一个表psverify_interaction

mysql> show create table psverify_interaction\G
*************************** 1. row ***************************
       Table: psverify_interaction
Create Table: CREATE TABLE `psverify_interaction` (
  `interaction_id` int(11) NOT NULL AUTO_INCREMENT,
  `customer_id` int(11) NOT NULL,
  `time_stamp` datetime NOT NULL,
  `request_message_details` text,
  `verification_status` varchar(30) DEFAULT NULL,
  `latitutde` varchar(20) DEFAULT 'NA',
  `longitude` varchar(20) DEFAULT 'NA',
  `ip_address` varchar(45) DEFAULT 'NA',
  `batch_id` int(11) DEFAULT NULL,
  `interaction_channel` varchar(10) DEFAULT NULL,
  PRIMARY KEY (`interaction_id`),
  KEY `customer_id` (`customer_id`)
) ENGINE=MyISAM AUTO_INCREMENT=381845 DEFAULT CHARSET=latin1
1 row in set (0.02 sec)

现在我需要找到每个客户

1. 有效验证之间的平均天数
2. 有效验证之间的天数标准差

对于每个客户的有效验证之间的平均日期可以这样做

SELECT customer_id, 
DATEDIFF(MAX(time_stamp),MIN(time_stamp)) / (COUNT(time_stamp)-1) as 'avg days between valid verification'
FROM psverify_interaction 
AND verification_status = 'valid' 
GROUP BY customer_id;

现在我需要找到“每个客户的有效验证之间的天数标准差”，如何在查询中找到它

示例数据

SELECT interaction_id,customer_id,time_stamp FROM psverify_interaction WHERE customer_id = 352 and  verification_status = 'valid';
+----------------+-------------+---------------------+
| interaction_id | customer_id | time_stamp          |
+----------------+-------------+---------------------+
|          60809 |         352 | 2010-04-07 08:22:02 |
|          88703 |         352 | 2010-05-11 02:08:02 |
|          88888 |         352 | 2010-05-19 00:20:02 |
|          88889 |         352 | 2010-05-19 00:28:07 |
|          90024 |         352 | 2010-08-09 11:09:02 |
+----------------+-------------+---------------------+

因此，有效验证之间的平均日期可以像

一样计算

SELECT customer_id, DATEDIFF(MAX(time_stamp),MIN(time_stamp)) / (COUNT(time_stamp)-1) 
FROM psverify_interaction 
WHERE customer_id = 352
AND verification_status = 'valid' 
GROUP BY customer_id;