CREATE TABLE table_203_688 (id DECIMAL, "category" TEXT, "speed\ ( km/h ) " DECIMAL, "speed\ ( mph ) " DECIMAL, "vehicle" TEXT, "pilot" TEXT, "date" TEXT)

who was the pilot for the north american x-15 ?
SELECT "pilot" FROM table_203_688 WHERE "vehicle" = 'north american x-15'
SELECT "pilot" FROM "table_203_688" WHERE "vehicle" = 'north american x-15'