id,user_id,key,value
1,534,difficulty_estimator,fk
2,1143,difficulty_estimator,fk
3,1140,difficulty_estimator,fk
4,9,difficulty_estimator,fk
5,534,de_ordering,easiest_first
6,534,nl_ordering,easiest_first
7,534,es_ordering,easiest_first
8,9,es_ordering,easiest_first