On average how many caffeinated root beers are sold a day?
average = DIVIDE(COUNT(RootBeerID WHERE Caffeinated = 'TRUE'), COUNT(PurchaseDate)); caffeinated refers to Caffeinated = 'TRUE';
SELECT CAST(COUNT(T2.RootBeerID) AS REAL) / COUNT(DISTINCT T2.PurchaseDate) FROM rootbeerbrand AS T1 INNER JOIN rootbeer AS T2 ON T1.BrandID = T2.BrandID INNER JOIN `transaction` AS T3 ON T2.RootBeerID = T3.RootBeerID WHERE T1.Caffeinated = 'TRUE'