CREATE TABLE notifications (
    id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    user_id INT UNSIGNED NOT NULL,
    business_id INT UNSIGNED NOT NULL,
    type ENUM('budget_alert', 'invite', 'system') NOT NULL DEFAULT 'system',
    message VARCHAR(255) NOT NULL,
    is_read TINYINT(1) NOT NULL DEFAULT 0,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    CONSTRAINT fk_notifications_user FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
    CONSTRAINT fk_notifications_business FOREIGN KEY (business_id) REFERENCES businesses(id) ON DELETE CASCADE,
    INDEX idx_notifications_user (user_id, is_read)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;