Calculate the average quantity per sales from sales id 20 to 30.
average quantity = AVG(Quantity); SalesID BETWEEN 20 AND 30;
SELECT AVG(Quantity) FROM Sales WHERE SalesID BETWEEN 20 AND 30
database name:db_id sales
Customers table Customers Cols: Customer ID dtype integer, First Name dtype text, Middle Initial dtype text, Last Name dtype text, 
Employees table Employees Cols: Employee ID dtype integer, First Name dtype text, Middle Initial dtype text, Last Name dtype text, 
Products table Products Cols: Product ID dtype integer, Name dtype text, Price dtype real, 
Sales table Sales Cols: Sales ID dtype integer, SalesPerson ID dtype integer, Customer ID dtype integer, Product ID dtype integer, Quantity dtype integer, 
