Here we want to consider some transparent solution with two slight mistakes. Here is it (pay attention on commentaries):
Console
SELECT q.battle
FROM (
--Determine ships from Ships table which taking part in battles
SELECT Outcomes.battle, Outcomes.ship, Classes.country
FROM Classes INNER JOIN
Ships ON Classes.class = Ships.class INNER JOIN
Outcomes ON Ships.name = Outcomes.ship
UNION
--Determine leading ships from the Outcomes table
SELECT Outcomes.battle, Outcomes.ship, Classes.country
FROM Outcomes INNER JOIN
Classes ON Outcomes.ship = Classes.class
) AS q
GROUP BY q.battle
HAVING COUNT(q.country) >= 3;
We hope that you`ll easily find this two mistakes and correct it.
To return to discussion of exercise #70
go
Console
