2009/2/26 Steve Holden <st...@holdenweb.com> > Murray wrote: > [top-posting corrected] > > > -----Original Message----- > > From: Gary Herron [mailto:gher...@islandtraining.com] > > Sent: Thursday, February 26, 2009 1:46 AM > > To: mmcclaf; python-list@python.org > > Subject: Re: Queries > > > > mmcclaf wrote: > >> I have to make some queries for 4 tables I have. The following > >> relations are: > >> > >> Classes(class, type, country, numGuns, bore, displacement) > >> Ships (name, class, launched) > >> Battles (name, date) > >> Outcomes (ship, battle, result) > >> > >> The three queries I'm stuck on are the following: > >> > >> 1. Find the classes that have only one ship as a member of that class > >> (not all ships are listed in the Ship table) > > Investigate a GROUP BY solution that selects groups having a count of 1.
DISTINCT may be a simpler solution. > > > >> 2. Find the countries that had both battleships and battlecruisers > >> (those fall under type in Classes) > > Look at EXISTS for one possible solutions. > > >> 3. Find those ships that "lived to fight another day"; they were > >> damaged in one battle, but later fought in another. > >> > >From your model description I don't even see where the position and > attitude of each ship is stored, so I don't think I can give you any > help at all with this one. > > >> The best way for me to understand would be relational algebra for each > >> of the statements. > >> > > > > > > Sounds like a homework assignment. Good luck with it. > > > > It is, however I was able to get the first 8 done, I am struggling with > > these 3 particular ones. I have to make an SQL file based off of it, > so this > > seems to be a blockage in my works. > > > Good luck with the homework. Remember to acknowledge the help you've had > from this list (particularly your earlier issues: here you just have > hints). > > regards > Steve > -- > Steve Holden +1 571 484 6266 +1 800 494 3119 > Holden Web LLC http://www.holdenweb.com/ > > -- > http://mail.python.org/mailman/listinfo/python-list > -- - Bret
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