List all paper ID and its class type with more than 20 cited words.
class type refers to class_label; count(word_cited_id)>20
SELECT DISTINCT T1.paper_id, T1.class_label FROM paper AS T1 INNER JOIN content AS T2 ON T1.paper_id = T2.paper_id GROUP BY T2.paper_id, T1.class_label HAVING COUNT(T2.word_cited_id) > 20
CREATE TABLE cites
(
    cited_paper_id  TEXT not null,
    citing_paper_id TEXT not null,
    primary key (cited_paper_id, citing_paper_id)
);
CREATE TABLE paper
(
    paper_id    TEXT  not null
        primary key,
    class_label TEXT not null
);
CREATE TABLE content
(
    paper_id     TEXT not null,
    word_cited_id TEXT not null,
    primary key (paper_id, word_cited_id),
    foreign key (paper_id) references paper(paper_id)
);
