What is the engineer visit id of that fault log entry id?
SELECT T2.engineer_visit_id FROM Fault_Log AS T1 JOIN Engineer_Visits AS T2 ON T1.fault_log_entry_id   =   T2.fault_log_entry_id where T2.fault_log_entry_id  =   ( SELECT T1.fault_log_entry_id FROM Fault_Log AS T1 JOIN Engineer_Visits AS T2 ON T1.fault_log_entry_id   =   T2.fault_log_entry_id GROUP BY T1.fault_log_entry_id ORDER BY count ( * )  DESC LIMIT 1 ) 
engineer visit id of that fault log entry id refers to a JOIN operation between Fault_Log and Engineer_Visits tables on fault_log_entry_id; identifying the fault_log_entry_id with the most records (implying most visits or entries) before fetching the corresponding engineer_visit_id.