CREATE TABLE people (people_id DECIMAL, district TEXT, name TEXT, party TEXT, age DECIMAL)
CREATE TABLE debate_people (debate_id DECIMAL, affirmative DECIMAL, negative DECIMAL, if_affirmative_win others)
CREATE TABLE debate (debate_id DECIMAL, date TEXT, venue TEXT, num_of_audience DECIMAL)

Show the names of people who have been on the negative side of debates at least twice.
SELECT T2.name FROM debate_people AS T1 JOIN people AS T2 ON T1.negative = T2.people_id GROUP BY T2.name HAVING COUNT(*) >= 2
SELECT "T2"."name" FROM "debate_people" AS "T1" JOIN "people" AS "T2" ON "T1"."negative" = "T2"."people_id" GROUP BY "T2"."name" HAVING COUNT(*) >= 2