Database: products_gen_characteristics
Question: What are characteristic names used at least twice across all products?
SQL:
SELECT t3.characteristic_name FROM products AS t1 JOIN product_characteristics AS t2 ON t1.product_id  =  t2.product_id JOIN CHARACTERISTICS AS t3 ON t2.characteristic_id  =  t3.characteristic_id GROUP BY t3.characteristic_name HAVING count(*)  >= 2