How add unique key to existing table (with non uniques rows)
database, mysql, rdbms, unique-key
Solution
You can do as yAnTar advised
ALTER TABLE TABLE_NAME ADD Id INT AUTO_INCREMENT PRIMARY KEY
OR
You can add a constraint
ALTER TABLE TABLE_NAME ADD CONSTRAINT constr_ID UNIQUE (user_id, game_id, date, time)
But I think to not lose your existing data, you can add an indentity column and then make a composite key.
Problem
I want to add complex unique key to existing table. Key contains from 4 fields (`user_id`, `game_id`, `date`, `time`). But table have non unique rows. I understand that I can remove all duplicate dates and after that add complex key. Maybe exist another solution without searching all duplicate data. (like add unique ignore etc). UPD I searched, how can remove duplicate mysql rows - i think it's good solution. Remove duplicates using only a MySQL query?