Why setting the key constraints on column removes "NOT NULL" from it (MySQL)?
PolGraphic
I have the code to create a table:
DROP TABLE IF EXISTS `database`.`creatures_kinds` ;
CREATE TABLE IF NOT EXISTS `database`.`creatures_kinds` (
`id` INT UNSIGNED NOT NULL AUTO_INCREMENT,
`parent_id` INT UNSIGNED NULL,
`name_en` VARCHAR(255) NOT NULL,
PRIMARY KEY (`id`, `parent_id`),
INDEX `parent_id` (`parent_id` ASC),
CONSTRAINT `parent`
FOREIGN KEY (`parent_id`)
REFERENCES `database`.`creatures_kinds` (`id`)
ON DELETE RESTRICT
ON UPDATE CASCADE)
ENGINE = InnoDB;
What surprise me is that the newly created table looks like this: 
Why the parent_id is set to NOT NULL when I wrote NULL in the CREATE TABLE?
Does it has something to do with the PRIMARY KEY or FOREIGN KEY?
I guess that parent_id is an identifiable relation (it points to more general creature kind, e.g. from pigeon to bird, and it's NULL for top-level creature kinds).
user4003407
A
PRIMARY KEYis a unique index where all key columns must be defined asNOT NULL. If they are not explicitly declared asNOT NULL, MySQL declares them so implicitly (and silently). MySQL Manual
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