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. >> 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
