What is the highest River Mile that has a pool length of 42.2 miles or a lock/lift drop of 21 feet?
CREATE TABLE "downstream_pittsburgh_to_olmsted" (
  "locks_dam" text,
  "location_l" text,
  "river_mile" real,
  "lock_side" text,
  "lock_lift_drop_in_feet" text,
  "pool_length_miles" text
);
SELECT MAX("river_mile") FROM "downstream_pittsburgh_to_olmsted" WHERE "pool_length_miles"='42.2' AND "lock_lift_drop_in_feet"='21';