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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
MySQL - Pivot tables

If at all possible, you should normalise information in your database using Codd's principles of database normalisation. Basically, this means that you don't duplicate information, store information that can be recalculated based on other fields, or store more than one piece of information in a single cell of your table.

This is all well and good until you want to store (for example) information about a person with a list of his children; the solution is to use two tables, with one table being joined to the other when you select your data out of the database.

That's what we call a "one to many" mapping, and the situation becomes slightly more complex when it goes a stage further and we have a "many to many" mapping. In such a situation, the best solution is usually to provide a third table known as a pivot table.

The subject came up during yesterday's MySQL Course and I wrote an example that I've posted to the solutions centre here on this site. The example will appear on appropriate future courses, and the data is available for viewing on the module description page.

(written 2004-09-22, updated 2006-06-05)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
S154 - MySQL - Designing an SQL Database System
  [361] Binary Large Objects or bars - (2005-06-27)
  [375] Oops - I got my initial database design wrong - (2005-07-12)
  [494] MySQL - a score of things to remember - (2005-11-12)
  [515] MySQL - an FAQ - (2005-12-03)
  [666] Database design - get it right from first principles - (2006-04-02)
  [918] Databases needn't be frightening, hard or expensive - (2006-11-08)
  [937] Display an image from a MySQL database in a web page via PHP - (2006-11-22)
  [945] Code quality counts - (2006-11-26)
  [1423] MySQL - table design and initial testing example - (2007-11-06)
  [1575] Database design for a shopping application (MySQL) - (2008-03-15)
  [1771] More HowTo diagrams - MySQL, Tomcat and Java - (2008-08-24)
  [2053] What a difference a MySQL Index made - (2009-02-25)
  [2085] MySQL - licensing issues, even with using the name - (2009-03-16)
  [2204] Images in a database? How big is a database? (MySQL) - (2009-05-28)
  [2749] Delegate Question - defining MySQL table relationships as you create the tables - (2010-05-02)
  [3270] SQL - Data v Metadata, and the various stages of data selection - (2011-04-29)
  [3361] Blowing our own trumpet - MySQL resources - (2011-07-18)
  [3494] Databases - when to treat the rules as guidelines - (2011-10-23)
  [4426] FileMaker Day to Unix Time conversion - (2015-02-15)


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