mysql - 使用标准偏差删除异常值

Question

我使用下面的查询来删除离群值(1.5 倍 sd)。

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

但是它给出了这个错误:

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

不知道是什么意思。

Answer 1

你可以用另一个子选择来欺骗 MySQL 来做到这一点

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