CREATE TABLE `groups` (
`id` INT PRIMARY KEY,
`name` VARCHAR(255)
);
CREATE TABLE `users` (
`id` INT PRIMARY KEY,
`group_id` INT,
FOREIGN KEY (`group_id`) REFERENCES `groups`(`id`)
);
CREATE TABLE `appointments` (
`id` INT PRIMARY KEY,
`user_id` INT,
FOREIGN KEY (`user_id`) REFERENCES `users`(`id`)
);
SELECT a.*
FROM appointments a
JOIN users u ON a.user_id = u.id
WHERE u.group_id = (
SELECT group_id
FROM users
WHERE users.id = '<User ID what you need>' -- Replace with an actual user ID
);