ALTER TABLE table_name
ADD UNIQUE INDEX xxxx (字段1, 字段2, ......);
再给已有表添加唯一索引时一直添加不上,一直报错1071,通过查阅资料才知道是因为字段长度过大问题
可参考
https://blog.youkuaiyun.com/z404739140/article/details/83384830
https://blog.youkuaiyun.com/zhangyingchengqi/article/details/73249996