Article View: borland.public.interbase.sql
Article #11289Re: Selecting row in which a column value is maximum
From: Craig Stuntz TeamB
Date: Tue, 26 Nov 2002 16:43
Date: Tue, 26 Nov 2002 16:43
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2585 bytes
In article <3de2bb5b$1@newsgroups.borland.com>, eddielee@tropicsoft.com says... > If I am controlling the transaction, then I wouldn't be doing so by allowing > the index to be updated while I need to get the maximum value for my key > column. The index doesn't need to be in the process of being updated. Just the record. IB is a versioning database. There can be many records in the index which are not visible to your transaction. Consider this situation: o Your transaction starts (SNAPSHOT) o Other guy's transaction starts o Other guy inserts record which is at top of index o You do a MAX o IB returns the maximum record visible to your transaction, *not* the maximum record in the index (which your transaction can't see). > I will pass a transaction as part of my SQL statement that freezes > the table from being updated until I can get back my value. This is possible, but it will quickly become a bottleneck in a heavily multiuser situation. -Craig -- Craig Stuntz [TeamB] � Vertex Systems Corp. � Columbus, OH Delphi/InterBase Weblog : http://delphi.weblogs.com InterBase Perf. Monitor : http://delphi.weblogs.com/IBPerformanceMonitor InterBase PLANalyzer 1.1: http://delphi.weblogs.com/IBPLANalyzer
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X-Google-Language: ENGLISH,ASCII X-Google-Thread: 114a0e,60a1aedc82f6444 X-Google-Attributes: gid114a0e,public X-Google-ArrivalTime: 2002-11-26 09:03:24 PST From: Craig Stuntz [TeamB] <cstuntz@nospamplease.com (but use vertexsoftware to email)> Newsgroups: borland.public.interbase.sql Subject: Re: Selecting row in which a column value is maximum Date: Tue, 26 Nov 2002 11:43:15 -0500 Message-ID: <MPG.184d6eb1c4e6ba7498a277@newsgroups.borland.com> References: <3de051cf@newsgroups.borland.com> <3de0d0f0$1@newsgroups.borland.com> <MPG.184c120210a6b55a98a253@newsgroups.borland.com> <3de24925@newsgroups.borland.com> <MPG.184c1b6154274d7b98a260@newsgroups.borland.com> <3de27571$1@newsgroups.borland.com> <MPG.184c493d33d5246b98a267@newsgroups.borland.com> <3de2bb5b$1@newsgroups.borland.com> Organization: Vertex Systems Corporation X-Newsreader: MicroPlanet Gravity v2.60 NNTP-Posting-Host: 65.86.87.242 X-Trace: newsgroups.borland.com 1038328901 65.86.87.242 (26 Nov 2002 08:41:41 -0800) Lines: 31 Path: arc1-ca.pugleaf.net!archiver1.google.com!news1.google.com!sn-xit-02!sn-xit-05!sn-xit-06!sn-xit-08!supernews.com!newsfeed.news2me.com!dfw3-feed1.news.algx.net!jfk3-feed1.news.algx.net!allegiance!news.maxwell.syr.edu!nntp-relay.ihug.net!newsfeeds.ihug.co.nz!ihug.co.nz!newsgroups.borland.com!not-for-mail