SELECT year FROM festival_detail GROUP BY year HAVING COUNT(*) > 1
List the year in which there are more than one festivals.
CREATE TABLE festival_detail (
    festival_id number,
    festival_name text,
    chair_name text,
    location text,
    year number,
    num_of_audience number
)

CREATE TABLE artwork (
    artwork_id number,
    type text,
    name text
)

CREATE TABLE nomination (
    artwork_id number,
    festival_id number,
    result text
)