Table: aircraft_history
Columns: aircraft
introduced
retired
seating
notes

Question: When was the aircraft introduced that could seat 115 people?
SQL: SELECT AVG("introduced") FROM aircraft_history WHERE "seating" = '115'

Question: What year was the aircraft retired when it was replaced by 737-300s?
SQL: SELECT "retired" FROM aircraft_history WHERE "notes" = 'replaced by 737-300s'

Question: What aircraft was introduced in 2004 and has a retired of —?
SQL: SELECT "aircraft" FROM aircraft_history WHERE "retired" = '—' AND "introduced" = 2004

Question: Which aircraft has 148/9 seating?
SQL: SELECT "aircraft" FROM aircraft_history WHERE "seating" = '148/9'

Question: How many people can be seated on the aircraft that was introduced in 2008 and has notes of in service?
SQL: SELECT "seating" FROM aircraft_history WHERE "notes" = 'in service' AND "introduced" = 2008