I see Connor has explained how a unique column can have a skewed data distribution. To answer the second paragraph - you don't have to worry about the timing of the histogram/index builds.
However, a though I've just had, it is possible that when Oracle builds the histogram, it MAY be able to use the index to avoid some of the cost of processing if you choose to COMPUTE a histogram for a non-null column. If you find this to be true, let us know. 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: 09 February 2003 21:20 > >Uniqueness indicates that there are less skewed values correct! Under what circumstances would a skewed column value for a unique column exist. > >Another question, what about histograms on indexes itself? If histograms are generated on columns with skewed values, does it matter when the indexes are generated, before or after? Do indexes on these columns need to be rebuilt. > >Thanks > > -- 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).
