Show the name and theme for all concerts and the number of singers in each concert.
create table singer_in_concert (concert_id varchar, PRIMARY KEY (concert_id)); create table concert (concert_name varchar, theme varchar, concert_id varchar, PRIMARY KEY (concert_name))
select t2.concert_name, t2.theme, count(*) from singer_in_concert as t1 join concert as t2 on t1.concert_id = t2.concert_id group by t2.concert_id