It's worth mentioning a frequently overlooked point that even if a column has a unique constraint (whether or not declared and/or supported by an index) then if it has a skewed pattern of values the optimiser can use a histogram to optimise a queries that target a range.
(NB The grammar suggests that the word "not" was intended as the last word of the first line of (b) below). Regards Jonathan Lewis http://www.jlcomp.demon.co.uk Coming soon one-day tutorials: Cost Based Optimisation Trouble-shooting and Tuning Indexing Strategies (see http://www.jlcomp.demon.co.uk/tutorial.html ) ____UK_______March 19th ____USA_(FL)_May 2nd Next Seminar dates: (see http://www.jlcomp.demon.co.uk/seminar.html ) ____USA_(CA, TX)_August The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html -----Original Message----- To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> Date: 08 February 2003 10:44 > >b) The number of distinct/duplicate values should >really be relevant - its whether you will regularly >need to probe a table using column values that are >skewed in such a way as to have the optimizer make >poor assumptions about their distribution. > -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jonathan Lewis INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
