MySQL 8.0

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-- data.sql

-- inserting sample rows if empty

INSERT INTO users(username, password, name, last_name, department, salary, age, email, enabled)
SELECT *
FROM (VALUES ROW ('mickey_m', '$2y$10$i5SJc2KAriHGn7Dz2rRQHuQ3JfBxlzMaPVKP1YdEJCukryDY9NbVC',
              'Mickey', 'Mouse', 'sales', 180000, 95, 'mickey_m@gmail.com', 1),

ROW ('donald_d', '$2y$10$E6SHpAN0aZGQ43HAO.TPiO27kDKXOGIgDc8xWDJdl2Prn2wzQzz5y',
              'Donald', 'Duck', 'information technology', 190000, 89, 'donald_d@outlook.com', 1),

ROW ('scrooge_m', '$2a$10$ycVpl2BSD6o19wa3xXtmrOxc8qZjwoIk.e3oZqgQBOE.3NHANAYqa',
              'Scrooge', 'McDuck', 'board of directors', 700000, 76, 'scrooge@gmail.com', 1),

ROW ('minerva_m', '$2y$10$sLgPImwI1WR5KZ98AFPHHut6MvbDoOdBnDC232oLRfejVsganoVyC',
              'Minerva', 'Mouse', 'sales', 180000, 95, 'minnie_m@outlook.com', 1),

ROW ('goofus_d', '$2y$10$uRP3KtW/yviK.H2VazCECOEQdZxZUZNqHqy/bL4kZgmaBCdprNeE2',
              'Goofus', 'Dawg', 'information technology', 190000, 91, 'goofy@gmail.com', 1),

ROW ('daisy_d', '$2a$10$mYfix0eIUMIWeTz6kM5.vuI/1demwzsvnY/mSgp5W6rcQVjc3Eyny',
              'Daisy', 'Duck', 'human resources', 165000, 86, 'daisy@outlook.com', 1))

AS sample_rows

WHERE NOT EXISTS(SELECT NULL FROM users);

-- ensuring the required roles exist

INSERT IGNORE INTO roles(role)
VALUES ('USER'),
       ('ADMIN');

-- filling the @JoinTable: all users must be USERs

INSERT IGNORE INTO user_role
SELECT users.id, roles.id
FROM users
         JOIN roles ON roles.role = 'USER';

-- filling the @JoinTable: the first user must also be an ADMIN

INSERT IGNORE INTO user_role
SELECT users.id, roles.id
FROM users
         JOIN roles ON roles.role = 'ADMIN' ORDER BY users.id LIMIT 1;

SELECT * FROM user_role;

Records: 6  Duplicates: 0  Warnings: 0

Records: 2  Duplicates: 0  Warnings: 0

Records: 6  Duplicates: 0  Warnings: 0

Records: 1  Duplicates: 0  Warnings: 0

user_id	role_id
1	1
2	1
3	1
4	1
5	1
6	1
1	2