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Re: trigger not acting as expected
Posted by: irek kordirko
Date: May 26, 2012 12:26PM

Matteo Tassinari Wrote:
-------------------------------------------------------
>
> IF NEW.nome_utente IS NULL OR NOT NEW.nome_utente
> THEN
> SET NEW.id_user_sgs = 1;
> SET NEW.nome_utente = 'SYSTEM';
> END IF;
> END $$
>

Nome_utente is certainly a string (varchar).
If string is not empty, NOT string gives always true.
Look at simple example:

drop table xxx;
create table xxx(
  name varchar( 10 )
);

insert into xxx values( null ), ( 'tom' ), ( 'john' );

select name,
       case when name is null or not name
            then 'null or 0' 
            else 'not null and not 0' 
       end result
from xxx;

+------+-----------+
| name | result    |
+------+-----------+
| NULL | null or 0 |
| tom  | null or 0 |
| john | null or 0 |
+------+-----------+
3 rows in set, 2 warnings (0,00 sec)

mysql> show warnings;
+---------+------+------------------------------------------+
| Level   | Code | Message                                  |
+---------+------+------------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'tom'  |
| Warning | 1292 | Truncated incorrect DOUBLE value: 'john' |
+---------+------+------------------------------------------+
2 rows in set (0,00 sec)


MySql tries to convert the string to a number, but when conversion is impossible the result of casting is 0.



Edited 1 time(s). Last edit at 05/26/2012 12:29PM by irek kordirko.

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Re: trigger not acting as expected
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May 26, 2012 12:26PM


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