A Database Error Occurred

Error Number: 1055

Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'freegames4rest.games_category.category' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

SELECT `game_id`, `category` FROM (`games_category`) WHERE `game_id` IN ('chicken_invaders_4_ultimate_easter_edition', 'chicken_invaders_4_ultimate_omelette_christmas_edition', 'chicken_invaders_4', 'chicken_invaders_2_cdhristmas_edition', 'chicken_invaders_3_revenge_yolk_easter', 'chicken_invaders2') GROUP BY `game_id`