MySQL error in file: /engine/modules/genre.php at line 9

Error Number: 1055

The Error returned was:
Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'ibolit.litres_data.genre_names' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

SQL query:

SELECT genre, genre_names FROM litres_data GROUP BY genre ORDER BY genre_names