Making the easy look difficult or is it the other way round


The one thing that my MSc course has taught me is that things I thought were simple – such as SQL – are in fact fiendishly difficult in the hands of an examiner and with a clock ticking against you.

Simple queries like SELECT Name FROM ListOfNames just are not where it is at.

Here is one exercise I found on the web that I was not able to solve (I gave up after half an hour).


The database of naval ships that took part in World War II is under consideration. The database has the following relations:
Classes(class, type, country, numGuns, bore, displacement)
Ships(name, class, launched)
Battles(name, date)
Outcomes(ship, battle, result)
Ships in classes are arranged to a single project. A class is normally assigned the name of the first ship in the class under consideration (head ship); otherwise, the class name does not coincide with any ship name in the database.
The Classes relation includes the class name, type (bb for a battle ship, or bc for a battle cruiser), country where the ship was built, number of main guns, gun caliber (diameter of the gun barrel, in inches), and displacement (weight in tons). The Ships relation includes the ship name, its class name, and launch year. The Battles relation covers the name and date of a battle the ships participated; while the result of their participation in the battle (sunk, damaged, or unharmed – OK) is in the Outcomes relation. Note: the Outcomes relation may include the ships not included in the Ships relation.


Point out the battles in which at least three ships from the same country took part.