使用标准偏差使用mysql删除异常值

Question

我使用下面的查询来删除异常值（是sd的1.5倍）。

DELETE FROM sv_condition_sw 
WHERE snow_mountain > (
    SELECT AVG(snow_mountain)+1.5*STDDEV(snow_mountain) 
    FROM sv_condition_sw 
    WHERE lud='2012-11-28' AND res_id=769)
AND lud='2012-11-28' 
AND res_id=769

然而它出现了这个错误：

查询：delete FROM sv_condition_sw WHERE snow_mountain > (SELECT AVG(snow_mountain)+1.5*STDDEV(snow_mountain) FROM sv_condition_sw WHER...

Error Code: 1093
You can't specify target table 'sv_condition_sw' for update in FROM clause

我不知道这意味着什么。

Answer 1

您可以使用另一个子选择

来欺骗MySQL

DELETE FROM sv_condition_sw 
WHERE snow_mountain > (select * from (SELECT AVG(snow_mountain)+1.5*STDDEV(snow_mountain) 
                                      FROM sv_condition_sw 
                                      WHERE lud='2012-11-28' 
                                      AND res_id=769) x)
 AND lud='2012-11-28' AND res_id=769