Delete duplicated mysql rows with no primary key

Question

Hi i have a mysql table without primary key and i need to delete the duplicated rows. how can i do so?

user_id category_id
1            2
1            3
1            4
1            2
2            2
2            3
2            2

Answer 1

 CREATE TABLE temp SELECT DISTINCT * FROM tablename;
 ALTER TABLE tablename RENAME junk;
 ALTER TABLE temp RENAME tablename;