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  1. #1
    Join Date
    Feb 2010
    Posts
    1

    Unanswered: how to display 2 columns with the same column name but different value?

    detailed problem is as follow:

    Here is a schema about battleships and the battles they fought in:

    Ships(name, yearLaunched, country, numGuns, gunSize, displacement)
    Battles(ship, battleName, result)

    A typical Ships tuple would be:


    ('New Jersey', 1943, 'USA', 9, 16, 46000)

    which means that the battleship New Jersey was launched in 1943; it belonged to the USA, carried 9 guns of size 16-inch (bore, or inside diameter of the barrel), and weighted (displaced, in nautical terms) 46,000 tons. A typical tuple for Battles is:


    ('Hood', 'North Atlantic', 'sunk')

    That is, H.M.S. Hood was sunk in the battle of the North Atlantic. The other possible results are 'ok' and 'damaged'.

    Write the following queries:

    1. List all the pairs of countries that fought each other in battles. List each pair only once, and list them with the country that comes first in alphabetical order first.

    2. For the battle of Surigao Strait, for each country engaged in that battle (had one or more battleships participating), give the number of its battleships that were sunk. Note: this question is very tricky. In particular, you need to deal with the (historical) case that a country engaged in the battle but did not have any ships sunk.

  2. #2
    Join Date
    May 2005
    Location
    South Africa
    Posts
    1,365
    Provided Answers: 1
    What have you done so far (show the query)
    where do you get stuck?

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