Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 5B2B69F9F6C for ; Sat, 10 Nov 2007 20:23:47 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-maia, port 10024) with ESMTP id 07739-09 for ; Sat, 10 Nov 2007 20:23:38 -0400 (AST) Received: from web54302.mail.re2.yahoo.com (web54302.mail.re2.yahoo.com [206.190.49.112]) by postgresql.org (Postfix) with SMTP id 386829F9A5F for ; Sat, 10 Nov 2007 20:23:44 -0400 (AST) Received: (qmail 15460 invoked by uid 60001); 11 Nov 2007 00:23:43 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:Date:From:Subject:To:MIME-Version:Content-Type:Content-Transfer-Encoding:Message-ID; b=gIwNnRJzRPRgr+x8HKGi7za8DiHfQSv+IF4cBy76l92JaTojlOAeo+GlAtw+qfQWHnnim38eijzY7mxWQMb/MN4T6ovrNq9WuTh4j8AqUYi0L02J/uSGdVFXWy7OS1L67l/dsXWZqaeRTqqlzI1z2e43G3MqBwkAbp9g4mxJnQk=; X-YMail-OSG: Lq_FEz8VM1lk96W1ynsjy5ImOgnrAJRPuGVJazj5i4hs68QOQHlmbmivbub34lcqQt.EWBwrlt0QA4DfZbCwsjde_0_ZOTz5H7u_4wkEKt7LdMJUH4VGgzStf61d2rcXbj6Ioy9FIdrA6jK6tAg1O8Qz9w-- Received: from [203.113.17.177] by web54302.mail.re2.yahoo.com via HTTP; Sat, 10 Nov 2007 16:23:42 PST Date: Sat, 10 Nov 2007 16:23:42 -0800 (PST) From: chester c young Subject: general question on optimizer To: sql pgsql MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Message-ID: <994792.8624.qm@web54302.mail.re2.yahoo.com> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200711/43 X-Sequence-Number: 29571 I have found that in many complex queries left join is exponentially faster than a (not) exists clause. I don't understand why, generally speaking, this is so frequently so effective. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com