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An occasional chance, and reducing data to manageable levels

If there's a 1 in 5 (20%) chance of it being a dry day at the moment, a 20% chance of it not being freezing cold, and a 20% chance of me having a day that I'm not training or otherwise involved, then it follows (since the conditions aren't related) that there's just a 1 in 125 or less that 1% chance of all three co-inciding. A.k.a. "fat chance".

Which is why you would have found me and Lisa, yesterday, re-roofing the conservatory / store room in which newsletters, envelopes, cables and 101 other business supplies are kept. The plastic sheeting on the roof of this '60s addition to our place was - to put it mildly - life expired and there was a real danger of some of the things kept in there getting damaged so we simply couldn't wait for a co-incidence of three 1-in-5s. "Between showers" is, I think, the best way to describe what we did; it was a darned sight dryer that the last few days which have lead, once again, to the formation of Lake Melksham.

Interestingly, SQL SELECT commands also use this principle of "a proportion of a proportion is a tiny bit of data" to reduce the amount of information supplied back to the using application by a database. In a select command, you specify which columns you want, and you also specify which rows you want. Which leads to a rapid data reduction. For example, if you have a 10 Mbyte database table and you select just 4 columns out of 20, and then just 100 rows out of 10000, your result set will be just 20k.

(written 2005-12-04, updated 2006-06-09)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
G100 - Well House Consultants - Introduction to Melksham
  [3932] River nearly bursting its banks in Melksham - (2012-11-23)
  [3696] Melksham government and business organisations - (2012-04-14)
  [3344] Repost - some useful pages on our site - (2011-07-04)
  [3232] Around and about Melksham in more pictures - (2011-04-05)
  [2704] A walk within without - Melksham Without - (2010-04-02)
  [2350] Ten years in Melksham - looking forward to ten more. - (2009-08-11)
  [2329] Great to be in Melksham - (2009-08-08)
  [1725] A future vision for Melksham - (2008-07-27)
  [1341] Moving to Melksham? Househunting map. - (2007-09-09)
  [866] A lazy programmer is a good programmer - (2006-09-15)
  [847] Image maps for navigation - a straightforward example - (2006-08-28)
  [676] Melksham, Wiltshire - (2006-04-08)
  [322] More maps - (2005-05-23)
  [291] Why are we no. 404 - (2005-04-25)
  [269] Free parking for short errands in Melksham - (2005-04-05)

S157 - More MySQL commands
  [4481] Extracting data from backups to restore selected rows from MySQL tables - (2015-05-01)
  [3270] SQL - Data v Metadata, and the various stages of data selection - (2011-04-29)
  [3061] Databases - why data is split into separate tables, and how to join them - (2010-11-20)
  [2647] Removing duplicates from a MySQL table - (2010-02-22)
  [2645] Optimising and caching your MySQL enquiries - (2010-02-22)
  [2644] Counting rows in joined MySQL tables - (2010-02-22)
  [2643] Relating tables with joins in MySQL - (2010-02-21)
  [2448] MySQL - efficiency and other topics - (2009-10-10)
  [2259] Grouping rows for a summary report - MySQL and PHP - (2009-06-27)
  [2110] MySQL - looking for records in one table that do NOT correspond to records in another table - (2009-03-31)
  [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23)
  [1735] Finding words and work boundaries (MySQL, Perl, PHP) - (2008-08-03)
  [1574] Joining MySQL tables revisited - finding nonmatching records, etc - (2008-03-15)
  [1331] MySQL joins revisited - (2007-09-03)
  [1235] Outputting numbers as words - MySQL with Perl or PHP - (2007-06-17)
  [1213] MySQL - the order of clauses and the order of actions - (2007-06-01)
  [673] Helicopter views and tartans - (2006-04-06)
  [591] Key facts - SQL and MySQL - (2006-02-04)
  [581] Saving a MySQL query results to your local disc for Excel - (2006-01-29)
  [572] Giving the researcher power over database analysis - (2006-01-22)
  [567] Combining similar rows from a MySQL database select - (2006-01-17)
  [515] MySQL - an FAQ - (2005-12-03)
  [513] MySQL - JOIN or WHERE to link tables correctly? - (2005-12-01)
  [502] SELECT in MySQL - choosing the rows you want - (2005-11-22)
  [494] MySQL - a score of things to remember - (2005-11-12)
  [449] Matching in MySQL - (2005-09-24)
  [279] Getting a list of unique values from a MySQL column - (2005-04-14)
  [159] MySQL - Optimising Selects - (2004-12-21)
  [158] MySQL - LEFT JOIN and RIGHT JOIN, INNER JOIN and OUTER JOIN - (2004-12-20)


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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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