concept of domains and subdomains for small database entities - mysql

Question

recently I learned a concept called by my teacher "Domains and subdomains" in which small tables are generalized in which less than 5000 data or rows will be saved, I show you an example:
Entities
enter image description here
level dates:
id_level description
01 continent
02 country
03 state
domain dates
id_domain detail level parent
01 America 01 -
02 USA 02 01
03 Europe 01 -
04 Africa 01 -
05 UK 02 03
06 Aberdeen 03 05
If this concept has another name, it would help me a lot to know it.
Then we had to make an abstraction of this and take it to common entities like the following example:
enter image description here
level dates:
id_level description
01 address
02 phone
03 gender
domain dates
id_domain detail level parent
01 male 03 -
02 female 03 -
03 mobile phone 02 -
04 home address 01 -
05 home phone 02 -
06 work address 01 -
Person dates
id_person name phone_type phone_value address_type adress_value gender
01 Jhon 03 39249927 06 a place... 01
02 Mary 05 2489540300 04 a place2... 02
but i get an error saying, the duplicate key name when i try to make the relation
ALTER TABLE person
ADD CONSTRAINT FK_PERSON_DOMAIN
FOREIGN KEY (address_type)
REFERENCES domain(id_domain);
Error
Duplicate key name 'FK_PERSON_DOMAIN'
Something I should add is that I already did the nesting with phone_type, after this it does not let me nest the other two attributes as shown in the diagram
This is the relationship that worked perfectly:
ALTER TABLE person
ADD CONSTRAINT FK_PERSON_DOMAIN
FOREIGN KEY (phone_type)
REFERENCES domain(id_domain);

Answer 1

I call those "lookup tables." They usually have characteristics of having a small number of rows, and also they don't change frequently. They may have an integer id primary key, or they may have a natural primary key.
The error you got about the duplicate key name is caused by the rule that constraint names must be unique across all tables in a schema. In other words, there must be only one constraint named FK_PERSON_DOMAIN_PERSON in the schema.
You said you already created a constraint with this name for the phone_type column. If you want another constraint for the address_type column, you must choose a different name for that constraint.
Here's an example of what I mean:
ALTER TABLE person
ADD CONSTRAINT FK_PERSON_PHONE
FOREIGN KEY (phone_type)
REFERENCES domain(id_domain);
ALTER TABLE person
ADD CONSTRAINT FK_PERSON_ADDRESS
FOREIGN KEY (address_type)
REFERENCES domain(id_domain);
See that the constraint names are different.