CREATE TABLE people (people_id DECIMAL, sex TEXT, name TEXT, date_of_birth TEXT, height DECIMAL, weight DECIMAL)
CREATE TABLE candidate (candidate_id DECIMAL, people_id DECIMAL, poll_source TEXT, date TEXT, support_rate DECIMAL, consider_rate DECIMAL, oppose_rate DECIMAL, unsure_rate DECIMAL)

which poll source does the highest oppose rate come from?
SELECT poll_source FROM candidate ORDER BY oppose_rate DESC LIMIT 1
SELECT "poll_source" FROM "candidate" ORDER BY "oppose_rate" DESC NULLS LAST LIMIT 1