Mysql-MySQL deletes duplicate data (two fields)

The userID and movieID fields in table full determine a unique data record. The table contains a small amount of duplicate data and a large amount of non-duplicate data. In duplicate data, the preference column and timestamp column are not empty and need to be retained. what should we do if the preference column and timestamp column are empty? Beginner, hope the answer is detailed :) grateful + ------------ + --------- + ------ + ----- + --------- + ------- + | Field | Type | Null | Key | Default... mysql duplicate data database

The userID and movieID fields in table full determine a unique data record.
The table contains a small amount of duplicate data and a large amount of non-duplicate data.
In duplicate data, the preference column and timestamp column are not empty and need to be retained. what should we do if the preference column and timestamp column are empty?
For beginners, I hope the answer is detailed. :) I am very grateful.
+ ------------ + --------- + ------ + ----- + --------- + ------- +
| Field | Type | Null | Key | Default | Extra |
+ ------------ + --------- + ------ + ----- + --------- + ------- +
| UserID | int (11) | NO | 0 |
| MovieID | int (11) | NO | 0 |
| Preference | int (11) | YES | NULL |
| Timestamp | int (11) | YES | NULL |
+ ------------ + --------- + ------ + ----- + --------- + ------- +