instruction: How many staffs have contacted with each engineer? Give me a bar chart grouping by each engineer's first name.
response: SELECT first_name, COUNT(first_name) FROM Staff AS T1 JOIN Engineer_Visits AS T2 ON T1.staff_id = T2.contact_staff_id JOIN Maintenance_Engineers AS T3 ON T2.engineer_id = T3.engineer_id GROUP BY first_name