What is the percentage of furniture orders that were shipped through first class in 2013 at the Central superstore?
furniture refers to Category = 'Furniture'; shipped through first class in 2013 refers to ship mode = 'first class' and "Ship Date" = '2013%'; percentage = divide(sum(Order ID) when Category = 'Furniture' and "Ship Date" = '2013%', sum(Order ID)) as percentage
SELECT CAST(SUM(CASE  WHEN T1.`Ship Mode` = 'First Class' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM central_superstore AS T1 INNER JOIN product AS T2 ON T1.`Product ID` = T2.`Product ID` WHERE T2.Category = 'Furniture' AND STRFTIME('%Y', T1.`Ship Date`) = '2013'