Robert Klemme wrote: > 2007/5/23, Becker, Holger <[EMAIL PROTECTED]>: > > Daniel Castro wrote: > > > > > Hi, > > > > > > I have some queries doing a SCAN. I identify then and I > > > create a index. > > > > > > For example: > > > > > > explain SELECT PSV.PSV_COD , PSV.PSV_APEL , > > > PSV.PSV_TRAT , PSV.PSV_TIPO FROM PSV WHERE ( > > > PSV.PSV_TIPO<> 'I' ) ORDER BY > > > PSV.PSV_APEL ASC > > > > > > Results: > > > DBA PSV TABLE SCAN 1019 > > > DBA RESULT IS NOT COPIED , COSTVALUE IS 1019 > > > > > > I created a index on PSV.PSV_TIPO <> 'I' but the query is > > > scanning the > > > table again. > > > After the index xreatino I have to do some other thing? > > > > > > Best regards, > > > > Hi, > > > > there is nothing to do after index creation. > > The index would be used if the optimizer would estimate > less I/O costs > > for the possible index strategy. > > In your case the scan seems to be less expensive than the > index access. > > This would be the case if the condition PSV.PSV_TIPO <> 'I' is not > > very selective. > > Which is usually the case for *exclusions*. Also, that an index seek > can usually be done only for equality (i.e. col = 1) - for all others > typically scans of part or the whole index occur. > > Kind regards > > robert >
Hi, only one small remark on Roberts posting. MaxDB optimizer transforms conditions like col <> 1 on index or key columns to (col > 1 or col < 1). So the optimizer could use two different strategies for each part which could be better than the scan. Kind regards Holger Holger Becker MaxDB&liveCache SAP AG www.sap.com Sitz der Gesellschaft/Registered Office: Walldorf, Germany Vorstand/SAP Executive Board: Henning Kagermann (Sprecher/CEO), Léo Apotheker, Werner Brandt, Claus Heinrich, Gerhard Oswald, Peter Zencke Vorsitzender des Aufsichtsrats/Chairperson of the SAP Supervisory Board: Hasso Plattner Registergericht/Commercial Register Mannheim No HRB 350269 Diese E-Mail kann Betriebs- oder Geschäftsgeheimnisse oder sonstige vertrauliche Informationen enthalten. Sollten Sie diese E-Mail irrtümlich erhalten haben, ist Ihnen eine Kenntnisnahme des Inhalts, eine Vervielfältigung oder Weitergabe der E-Mail ausdrücklich untersagt. Bitte benachrichtigen Sie uns und vernichten Sie die empfangene E-Mail. Vielen Dank. This e-mail may contain trade secrets or privileged, undisclosed, or otherwise confidential information. If you have received this e-mail in error, you are hereby notified that any review, copying, or distribution of it is strictly prohibited. Please inform us immediately and destroy the original transmittal. Thank you for your cooperation. -- MaxDB Discussion Mailing List For list archives: http://lists.mysql.com/maxdb To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
