表注释

SELECT TABLE_COMMENT FROM information_schema.TABLES WHERE TABLE_SCHEMA = '5mzb' AND TABLE_NAME = 'user';
ALTER TABLE `user` COMMENT = '用户';

字段注释

SELECT COLUMN_NAME, COLUMN_COMMENT FROM `information_schema`.`COLUMNS`
WHERE TABLE_SCHEMA = 'sendcloud' AND TABLE_NAME = 'user_info' ORDER BY ORDINAL_POSITION;

ALTER TABLE `user`
CHANGE COLUMN `create_time`
`create_time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间' AFTER `expire_time`;

ALTER TABLE `user`
MODIFY COLUMN
`create_time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间' AFTER `expire_time`;

好傻 X 啊，只改个备注，却必须要把字段声明带上，增加出错的可能。