| SubqueriesA query can have subqueries. (Whether a query should have subqueries is a valid question.) Schema
create table Author(
    author_id int not null primary key,
    name varchar,
    birth_date date,
    birth_country varchar
);
create table Book(
    book_id int not null primary key,
    author_id int references Author,
    title varchar,
    year int
);
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