How to merge tables correctly?

Question

SQL

It is necessary to create two plates: department, users. When displaying a person, information about his department should be displayed. And when outputting a department, information about the employees in that department.

CREATE TABLE Users
(
    Id INT PRIMARY KEY AUTO_INCREMENT,
    DepartmentId INT,
    Age INT, 
    FirstName VARCHAR(20) NOT NULL,
    LastName VARCHAR(20) NOT NULL,
    Phone VARCHAR(20) NOT NULL UNIQUE,
    FOREIGN KEY (DepartmentId) REFERENCES Departments (id)
);
 
CREATE TABLE Departments
(
    Id INT PRIMARY KEY AUTO_INCREMENT,
    UserId INT,
    DepartmentName VARCHAR(20) NOT NULL,	
    FOREIGN KEY (UserId)  REFERENCES Users (Id)
);

It throws an error - Failed to open the referenced table 'departments' , but I don't understand anything. Help

Answer 1

first create the Departments table and then refer to it in the foreign key.
but since you are trying to implement cyclic foreign keys, I inform you that this is not possible. and what's more, it's not true. there are even DBMS that will write about it explicitly in the error text.