On 4/2/06, chris smith <dmagick@xxxxxxxxx> wrote: > On 4/2/06, Jim C. Nasby <jnasby@xxxxxxxxxxxxx> wrote: > > On Sat, Apr 01, 2006 at 11:23:37AM +1000, chris smith wrote: > > > On 4/1/06, Brendan Duddridge <brendan@xxxxxxxxxxxxxx> wrote: > > > > Hi Jim, > > > > > > > > I'm not quite sure what you mean by the correlation of category_id? > > > > > > It means how many distinct values does it have (at least that's my > > > understanding of it ;) ). > > > > Your understanding is wrong. :) What you're discussing is n_distinct. <rant> It'd be nice if the database developers agreed on what terms meant. http://dev.mysql.com/doc/refman/5.1/en/myisam-index-statistics.html The SHOW INDEX statement displays a cardinality value based on N/S, where N is the number of rows in the table and S is the average value group size. That ratio yields an approximate number of value groups in the table. </rant> A work colleague found that information a few weeks ago so that's where my misunderstanding came from - if I'm reading that right they use n_distinct as their "cardinality" basis.. then again I could be reading that completely wrong too. I believe postgres (because it's a lot more standards compliant).. but sheesh - what a difference! This week's task - stop reading mysql documentation. -- Postgresql & php tutorials http://www.designmagick.com/
