Exercise #39 page 3
It's said but true, the following query was accepted by the system until the last days:
Firstly, the queries, which perform joining the ships taken part in battles (Outcomes table) with the Ships table and Classes table accordingly, are being united. By the way, the predicate
These joins are not just surplus, they are wrong, as the description of the database says that in the Outcomes table can be ships that are absent from Ships table. That is, if not the leading ship is found, which is absent from the Ships table and which satisfies the task terms, then it will not get into the resulting set of the aforecited query.
Secondly, the predicate
Thirdly, I don't quite understand the condition: