CREATE TABLE furniture (furniture_id DECIMAL, name TEXT, num_of_component DECIMAL, market_rate DECIMAL)
CREATE TABLE furniture_manufacte (manufacturer_id DECIMAL, furniture_id DECIMAL, price_in_dollar DECIMAL)
CREATE TABLE manufacturer (manufacturer_id DECIMAL, open_year DECIMAL, name TEXT, num_of_factories DECIMAL, num_of_shops DECIMAL)

find the total market rate of the furnitures that have the top 2 market shares.
SELECT SUM(market_rate) FROM furniture ORDER BY market_rate DESC LIMIT 2
SELECT SUM("market_rate") FROM "furniture" ORDER BY "market_rate" DESC NULLS LAST LIMIT 2