Steve Holden steve at holdenweb.com
Thu Feb 26 13:51:50 CET 2009

Murray wrote:
[top-posting corrected]

> -----Original Message-----
> From: Gary Herron [mailto:gherron at islandtraining.com] 
> Sent: Thursday, February 26, 2009 1:46 AM
> To: mmcclaf; python-list at 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).

Steve Holden        +1 571 484 6266   +1 800 494 3119
Holden Web LLC              http://www.holdenweb.com/

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