Table: train_data
Columns: type
numbers
year_built
quantity_built
power_horsepower
max_speed_km_h

Question: What is the max speed of the unit with an 8+4 quantity built before 1971?
SQL: SELECT SUM("max_speed_km_h") FROM train_data WHERE "quantity_built" = '8+4' AND "year_built" < 1971

Question: What is the numbers of the thn unit with a power greater than 220?
SQL: SELECT "numbers" FROM train_data WHERE "power_horsepower" > 220 AND "type" = 'thn'

Question: What is the power of the unit built after 1995?
SQL: SELECT SUM("power_horsepower") FROM train_data WHERE "year_built" > 1995