--3.1 Select all warehouses.
--3.2 Select all boxes with a value larger than $150.
--3.3 Select all distinct contents in all the boxes.
--3.4 Select the average value of all the boxes.
--3.5 Select the warehouse code and the average value of the boxes in each warehouse.
--3.6 Same as previous exercise, but select only those warehouses where the average value of the boxes is greater than 150.
--3.7 Select the code of each box, along with the name of the city the box is located in.
--3.8 Select the warehouse codes, along with the number of boxes in each warehouse. 
    -- Optionally, take into account that some warehouses are empty (i.e., the box count should show up as zero, instead of omitting the warehouse from the result).
--3.9 Select the codes of all warehouses that are saturated (a warehouse is saturated if the number of boxes in it is larger than the warehouse's capacity).
--3.10 Select the codes of all the boxes located in Chicago.
--3.11 Create a new warehouse in New York with a capacity for 3 boxes.
--3.12 Create a new box, with code "H5RT", containing "Papers" with a value of $200, and located in warehouse 2.
--3.13 Reduce the value of all boxes by 15%.
--3.14 Remove all boxes with a value lower than $100.
-- 3.15 Remove all boxes from saturated warehouses.
-- 3.16 Add Index for column "Warehouse" in table "boxes"
    -- !!!NOTE!!!: index should NOT be used on small tables in practice
-- 3.17 Print all the existing indexes
    -- !!!NOTE!!!: index should NOT be used on small tables in practice
-- 3.18 Remove (drop) the index you added just
    -- !!!NOTE!!!: index should NOT be used on small tables in practice