yes, you'd have to alter the queries to use the new index. As I say it's very application dependent and does not always apply, but you can normally shoehorn any application to use it.
Phil On Wed, May 21, 2008 at 9:22 AM, Bof <[EMAIL PROTECTED]> wrote: > Hi Phil - > > Thanks for the suggestion. Might that involve possibly > changing queries in the web application hitting the > database so that it uses the new column, or would the > indexing on the new column take care of speeding up > the existing queries? > > cheers > Iain > -- > > > --- Phil <[EMAIL PROTECTED]> wrote: > > > What I've done in the past is to create extra > > columns which contain the > > reverse of a number/date used previously in an > > index. > > > > So, for instance if it's a simple INT column (A) and > > you know the max would > > be 9999999 for example, create an extra column and > > populate that with > > (10000000 - A) and use it as an ASC index. > > > > Same can be done with dates. > > > > Not always applicable, but it works and is fairly > > easy to implement. > > > > Phil > > > > On Tue, May 20, 2008 at 2:20 PM, Bof > > <[EMAIL PROTECTED]> wrote: > > > > > Hi all - > > > Is there a good workaround for mysql's lack of > > 'DESC' > > > functionality when creating an index? > > > > > > I'm looking at migrating an Oracle RAC database to > > > mysql (InnoDB or Cluster - testing both at the > > > moment), and the Oracle database uses a lot of > > > multi-column indexes with some colums indexed in > > > descending order. > > > > > > If I can't emulate the descending index colums > > somehow > > > it's likely to seriously impact performance and > > > possibly derail the prospect of migration - help! > > > > > > cheers > > > Iain > > > -- > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > MySQL General Mailing List > > > For list archives: http://lists.mysql.com/mysql > > > To unsubscribe: > > > http://lists.mysql.com/[EMAIL PROTECTED] > > > > > > > > > > > -- > > Help build our city at http://free-dc.myminicity.com > > ! > > > > > > > -- Help build our city at http://free-dc.myminicity.com !
