Exercise #23 (tips and solutions)
To solve this exercise is generally used two approaches: first, the join and selecting the required row and second, check for hit maker in the two lists. The next incorrect solution implements the first approach:
This is another variant on the theme of "something one". Indeed, the model is unique, ie it is either a PC or laptop. Next rows are obtained as result of external joins:
However, there can be no rows such as:
As a result, the list contains only makers who make only one product type with the desired characteristics. However, the correct solution is simply adding the grouping by maker and model counting. We suggest you do it yourself.
To demonstrate the second approach, consider the following variant: