For what i understand, what you need to do is create this structure: Characteristic K Char_Code Char_Description
Continent K Con_Code Con_Description Country K Cot_Code Cot_Description Cot_Continent ( This is the code of a continent in the table continent) Country_Charact K Des_Country ( This is the code of a country in the table country) K Des_Characteristic ( This is the code of a characteristic in the table characteristic) This way you can define the characteristics 1 time and assign to a country as many or as few as you need. You may want to use innob tables to create the foreing key and to help them inforce them. Hope this is usefull Osvaldo Sommer -----Original Message----- From: David Blomstrom [mailto:[EMAIL PROTECTED] Sent: Saturday, May 29, 2004 5:57 PM To: [EMAIL PROTECTED] Subject: Re: Getting Oriented: Political versus Ecological Geography --- Peter Brawley <[EMAIL PROTECTED]> wrote: > >In the states table, should I list Colorado's > regions > >in three cells... Great Plains | Rocky Mountains | > >Colorado Plateau, or group them in one cell, like > >this: > > >Colorado | state | grasslands, Rocky Mountains, > >Colorado Plateau | co | cna | 5 > > >It gets even trickier, because I may link Colorado > to > >several regions, including ecological regions, > >physiographic provinces and political. > > Codd's first axiom is that all values shall be > atomic (yes, mysql sets & > enums break that rule). Putting your little set > 'grasslands, mountains, > plateau' in one column would make queries on those > items awkward. You might > want to bone up on normalisation (viz links at > http://www.artfulsoftware.com/dbresources.html). Thanks for the link. I've been studying some of the resources. I have an idea for another approach. If putting "grasslands, forests, mountains" in one cell is bad practice, then I may wind up with a table with hundreds of fields. Imagine one field filled with the names of the world's nations. Then imagine another field for tropical cloud forests, with three South American nations checked. A few northern nations are checked in the "Tundra" field, and so on. Obviously, there are going to be vast numbers of cells with no values at all. But what if I instead created several tables, one for each continent and listing only ecological regions associated with that continent. For example, the North America table might have just three rows, for the U.S., Canada and Mexico, with the following fields: tundra | boreal forest | eastern forests | Rocky Mountain forests | eastern grasslands | Great Plains | Sonora desert | California coastal | Pacific Northwest (there are actually a lot more.) The Africa table would have far more rows, for nations from Algeria to Zimbabwe, with fields that might look something like this: Sahara Desert | Sahel | Ethiopian mountains | tropical forest | woodlands | savanna Thus, North America and Africa will share no fields in common. However, North America and Eurasia will both share at least two fields - Tundra and Boreal Forest. So, if I create such tables for each continent, will I later be able to make a join that pulls up tundra in North America, Eurasia and Antarctica? Can I pull up the general term "grasslands" for all continents, or pull up Great Plains grasslands for just North America? Thanks. __________________________________ Do you Yahoo!? Friends. Fun. Try the all-new Yahoo! Messenger. http://messenger.yahoo.com/ -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] --- Incoming mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.692 / Virus Database: 453 - Release Date: 5/28/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.692 / Virus Database: 453 - Release Date: 5/28/2004 -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
