CREATE TABLE `users` (
    `id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    `username` VARCHAR(100),
    -- other user fields --
);

CREATE TABLE `permissions` (
    `id` INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    `name` VARCHAR(50) NOT NULL UNIQUE,
);

CREATE TABLE `users_permissions` (
    `id` INT NOT NULL AUTO_INCREMENT PRIMARY_KEY,
    `user_id` INT NOT NULL,
    `permission_id` INT NOT NULL
);

INSERT INTO `users` (DEFAULT, 'joe');
INSERT INTO `users` (DEFAULT, 'beth');
INSERT INTO `users` (DEFAULT, 'frank');

INSERT INTO `permissions` (DEFAULT, 'Administrator');
INSERT INTO `permissions` (DEFAULT, 'Write Blog');
INSERT INTO `permissions` (DEFAULT, 'Edit Blog');
INSERT INTO `permissions` (DEFAULT, 'Delete Blog');

-- joe gets all permissions
INSERT INTO `permissions` (DEFAULT, 1, 1);
INSERT INTO `permissions` (DEFAULT, 1, 2);
INSERT INTO `permissions` (DEFAULT, 1, 3);
INSERT INTO `permissions` (DEFAULT, 1, 4);

-- beth can write and edit
INSERT INTO `permissions` (DEFAULT, 2, 2);
INSERT INTO `permissions` (DEFAULT, 2, 3);

-- frank can only write
INSERT INTO `permissions` (DEFAULT, 3, 2);

const READ = 1;
const WRITE = 2;
const DELETE = 4;
...

read-only: 1
read-write: 3
read & delete, but not write: 5
and so on...

SELECT * FROM table t WHERE t.permission & required_permission