How can I solve this ER diagram for a database? - database

Question

I have question with a ER diagram I'm creating for a database, I basically have 2 tables, one is called 'Employee' and the other is called 'Store'. Each store has certain number of employees, I need to know in what store the employee is located. The thing is, A store is required to have a boss/manager who has to be one of the employees. The picture below shows how I made it. However when I create these tables on PostgreSQL I get an error because I'm referencing a table who has not been created yet.
This is how I'm trying to create the two tables, how can I solve this?
Any ideas?
create table Store(
store_id serial primary key,
storeName varchar(20),
employee_id int,
foreign key (employee_id) references Employee(employee_id)
);
create table Employee(
employee_id serial primary key,
firstname varchar(50),
lastname varchar(50),
address varchar(50)
email varchar(100),
store_id int,
foreign key (store_id) references Store(store_id)
);
Error:
SQL Error [42P01]: ERROR: relation "employee" does not exist

Answer 1

All you would have to do is create the foreign key constraints after the tables have been created like this
create table Store(
store_id serial primary key,
storeName varchar(20),
employee_id int
);
create table Employee(
employee_id serial primary key,
firstname varchar(50),
lastname varchar(50),
address varchar(50),
email varchar(100),
store_id int
);
alter table Store add constraint fk_store_employee_id foreign key (employee_id) references Employee(employee_id) DEFERRABLE INITIALLY DEFERRED;;
alter table Employee add constraint fk_employee_store_id foreign key (store_id) references Store(store_id) DEFERRABLE INITIALLY DEFERRED;;
the DEFERRABLE INITIALLY DEFERRED makes it that the constraint is checked at the end of the transaction otherwise you would get a foreign key constraint violation since the employee wouldn't exist when you create the store and the store wouldn't exist when you create the employee.
here is a working example https://www.db-fiddle.com/f/71b3KhwDMSgKmsWsbAeUTR/1
but even with the DEFERRABLE INITIALLY DEFERRED how would you know what id an employee and store is going to get?
i think you might be better off using a third table to store store managers like this
create table Store(
store_id serial primary key,
storeName varchar(20)
);
create table Employee(
employee_id serial primary key,
firstname varchar(50),
lastname varchar(50),
address varchar(50),
email varchar(100),
store_id int,
foreign key(store_id) references Store(store_id)
);
create table StoreManager (
store_id int,
employee_id int,
primary key(store_id, employee_id),
foreign key(store_id) references Store(store_id),
foreign key(employee_id) references Employee(employee_id)
);
this you can first create the store then the employee and then you can pair the two in the StoreManager table
here is a working example https://www.db-fiddle.com/f/71b3KhwDMSgKmsWsbAeUTR/2