MySQL忽略具有标准偏差的异常值

Question

我需要构建一个查询来计算平均值和计数，同时忽略标准偏差中的异常值。

Mysql 中有两个表（P 和 A），具有以下属性：

P = 付款：

Value_gbp
Paymentid
Account 
rfx_ref

A = 帐户：

Accountid
Entity_type
Settlment_model
rfx_ref

到目前为止，我得到了这个：

SELECT 
Account, 
COUNT(value_GBP) AS '# Of Payments', 
TRUNCATE(AVG(value_GBP),2) As 'Avg Value'
FROM payments, 

LEFT JOIN( 
SELECT STDDEV(value_gbp) as std_gbp
FROM payments, accounts 
WHERE payments.paymentid = accounts.acountid
AND Entity_type = 'company'
AND settlement_model = 'payment agent'
GROUP BY account
) outlier 

On payments.paymentid = accounts.acountid
WHERE payments.value_gbp<=outlier.std_gbp*2
AND Entity_type = 'company'
AND settlement_model = 'payment agent'
GROUP BY account

但它正在下降，说明：

On payments.paymentid = accounts.acountid

谁能帮帮我？

Answer 1

子查询需要选择accounts.accountid，然后你需要在JOIN条件下使用这个。

我也认为您对异常值的定义是错误的。它不应该超过 2 个标准偏差，它应该比平均值超过 2 个标准偏差。所以子查询需要同时返回平均值和标准差，然后你比较距离。

SELECT 
    account, 
    COUNT(value_GBP) AS '# Of Payments', 
    TRUNCATE(AVG(value_GBP),2) As 'Avg Value'
FROM payments 
JOIN( 
    SELECT accountid, AVG(value_gpb) AS avg_gbp, STDDEV(value_gbp) as std_gbp
    FROM payments, accounts 
    WHERE payments.paymentid = accounts.acountid
    AND Entity_type = 'company'
    AND settlement_model = 'payment agent'
    GROUP BY accountid
) outlier 
On payments.paymentid = outlier.accountid
JOIN accounts ON payments.paymentid = accounts.accountid
WHERE ABS(payments.value_gbp - outlier.avg_gpb) <= outlier.std_gbp*2
AND Entity_type = 'company'
AND settlement_model = 'payment agent'
GROUP BY account