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Re: Reading a field's default value from a trigger



>>>>> "Federico" == Federico Razzoli <federico_raz@xxxxxxxx> writes:

Federico> I'm not sure if I use a wrong syntax or I found a bug. But I can't read a column's default value from a trigger.
Federico> The trigger just checks if the INSERT is trying to set a column to its default value:

Federico> DELIMITER ||

Federico> CREATE TABLE `blog`
Federico> (
Federico> 	`created_by` CHAR(60) NOT NULL DEFAULT ''
Federico> );

Federico> CREATE TRIGGER `blog_default_created_by`
Federico> 	ON `blog`
Federico> 	FOR EACH ROW
Federico> BEGIN
Federico> 	IF NEW.`created_by` = DEFAULT(NEW.`created_by`) THEN
Federico> 		SET NEW.`created_by` = USER();
Federico> 	END IF;
Federico> END;

Federico> ||
Federico> DELIMITER ;

Federico> But when I try to INSERT a row I get an error:

Federico> MariaDB [test]> INSERT INTO `blog` SET `created_by` = '';
Federico> ERROR 1364 (HY000): Field 'created_by' doesn't have a default value

Federico> This problem disappears if I replace DEFAULT(NEW.`created_by`) with '', so I'm not in troubles - but in theory a default value may change, so using DEFAULT() is a better practice.

Federico> The syntax I'm using could be wrong, but I've tried all the alternatives which seemed to me possible, and they didn't work: DEFAULT, DEFAULT(`created_by`), DEFAULT('created_by').

This is a bug in how MariaDB / MySQL detects if a field has a default
value.  It's probably because of this is a trigger on 'new', which is
not something that is apparently not handled properly.

Do you want to try to fix it yourself?
(Shouldn't take many minutes ;)


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