Table schema:
CREATE TABLE Treatments (cost_of_treatment INTEGER); CREATE TABLE Professionals (first_name VARCHAR, last_name VARCHAR); CREATE TABLE Treatments (Id VARCHAR)

Question: What are the first name and last name of the professionals who have done treatment with cost below average?
SQL: SELECT DISTINCT T1.first_name, T1.last_name FROM Professionals AS T1 JOIN Treatments AS T2 WHERE cost_of_treatment < (SELECT AVG(cost_of_treatment) FROM Treatments)