Database model for hierarchy Country - Organization - Suborganization - User - mysql

Question

Good day, I need to create an organizational structure which should support following hierarchies:
Country - Organization - User
Country - Organization - Suborganization - User
I thought about having three tables. Table Country (column id is three-letter ISO 3166-1 alpha-3):
CREATE TABLE `country` (
`id` CHAR(3) NOT NULL,
`country` VARCHAR(40) NOT NULL,
PRIMARY KEY (`id`)
);
Table Organization:
CREATE TABLE `organization` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`country_id` CHAR(3) NOT NULL,
`parent_id` INT(11) NULL DEFAULT NULL,
`name` VARCHAR(40) NOT NULL,
PRIMARY KEY (`id`),
INDEX `idx_organization_1` (`parent_id` ASC),
CONSTRAINT `fk_customer_country_1`
FOREIGN KEY (`country_id`)
REFERENCES `country` (`id`)
ON DELETE CASCADE
ON UPDATE CASCADE,
CONSTRAINT `fk_organization_organization_1`
FOREIGN KEY (`parent_id`)
REFERENCES `organization` (`id`)
ON DELETE CASCADE
ON UPDATE CASCADE
);
Table User:
CREATE TABLE `user` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`organization_id` INT(11) NULL DEFAULT NULL,
`username` VARCHAR(45) NOT NULL,
`password` CHAR(32) NOT NULL,
PRIMARY KEY (`id`),
INDEX `idx_user_organization_1` (`organization_id` ASC),
CONSTRAINT `fk_user_organization_1`
FOREIGN KEY (`organization_id`)
REFERENCES `organization` (`id`)
ON DELETE CASCADE
ON UPDATE CASCADE);
Table Country exists to prevent an organization be assigned an unsupported country code. I don't want to use MySql's enum. Although I'm working with MySql currently I need my schema to be independent on the specific DB.
Is this good design or is there a better one? I doubt because of following questions. I can do it "somehow" but I'd like to know best practice approach.
A suborganization has a country code foreign key but country code is allready specified in the parent organization. I feel it's a kind of duplicity.
If I delete a row in table country will cascade delete fail if the DB attempts to delete suborganization before deleting it's parent organization?
Is null in foreign keys supported by all DBs? Organizations have null parent_id but parent_id is used in the self referencing forign key fk_organization_organization_1.
Country code used in foreign keys is CHAR(3). Would it be faster is it would be INT(3)?
I'd appreciate any ideas. Many thanks. Vojtech

Answer 1

I would make country_id nullable to avoid such duplication. Also
you can implement some application-level control to assure that at
least one of (country_id, parent_id) is not null.
Deletion must
be successfull as long as the both references defined with "ON
DELETE CASCADE" clause
All the DBs I have worked with support
nullable foreign keys: Oracle, DB2, MySQL, SQL Server, Postgre
The difference is most probably negligible