Table schema:
CREATE TABLE singer_in_concert (concert_id VARCHAR); CREATE TABLE concert (concert_name VARCHAR, theme VARCHAR, concert_id VARCHAR)

Question: What are the names , themes , and number of singers for every concert ?
SQL: 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