-- user_devices.id is a table-local AUTO_INCREMENT row key, not Snowflake.
-- Business identity remains (user_id, device_id). Existing Snowflake values stay; new rows continue from MAX(id)+1.

ALTER TABLE user_devices
    MODIFY COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (user_id, device_id)';