Question

I use the query below to delete outliers (1.5 times the 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

However it gives this error:

Query: 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

I do not know what it means.

Answer 1

You can trick MySQL to do this with another subselect

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