向表中添加唯一的键/索引及其对现有记录的影响

I have a table that was doing fine with no unique keys so far. This table is working fine but the code of inserting/updating/deleting procedures is getting a bit unreadable since conditions to recognize a correct entry in table are getting longer and longer, so I started to consider adding a new column with an unique ID to it.I have a table that was doing fine with no uniq