Return-Path: owner-postman Received: from localhost (localhost [127.0.0.1]) by nobozo.CS.Berkeley.EDU (8.6.4/8.6.3) with SMTP id BAA12774 for postgres-dist; Fri, 12 Nov 1993 01:42:36 -0800 Resent-From: POSTGRES mailing list Resent-Message-Id: <199311120942.BAA12774@nobozo.CS.Berkeley.EDU> Sender: owner-postman@postgres.Berkeley.EDU X-Return-Path: owner-postman Received: from faerie.CS.Berkeley.EDU (faerie.CS.Berkeley.EDU [128.32.149.14]) by nobozo.CS.Berkeley.EDU (8.6.4/8.6.3) with ESMTP id BAA12765 for ; Fri, 12 Nov 1993 01:42:35 -0800 Received: from localhost (localhost [127.0.0.1]) by faerie.CS.Berkeley.EDU (8.6.3/8.1B) with SMTP id BAA04093; Fri, 12 Nov 1993 01:42:16 -0800 Message-Id: <199311120942.BAA04093@faerie.CS.Berkeley.EDU> X-Authentication-Warning: faerie.CS.Berkeley.EDU: Host localhost didn't use HELO protocol From: aoki@postgres.Berkeley.EDU (Paul M. Aoki) To: Peter van Oosterom Cc: postgres@postgres.Berkeley.EDU Subject: Re: rewrite rule In-reply-to: Your message of Thu, 11 Nov 93 15:38:44 MET <199311111438.AA12842@fel.tno.nl> Date: Fri, 12 Nov 93 01:42:16 -0800 X-Sender: aoki@postgres.Berkeley.EDU Resent-To: postgres-dist@postgres.Berkeley.EDU X-Mts: smtp Resent-Date: Fri, 12 Nov 93 01:42:36 -0800 Resent-XMts: smtp Peter van Oosterom writes: > define rewrite rule r1 is > on retrieve to rel.a where current.a = "AAB" > do instead retrieve (a = "Y")\g the manual says (in its usual crystal-clear prose): When choosing between the rewrite and instance rule systems for a par- ticular rule application, remember that in the rewrite system current refers to a relation and some qualifiers whereas in the instance system it refers to an instance (tuple). in the rewrite system, this effectively means that the query is rewritten as retrieve (a = "Y") from current in rel where current.a = "AAB" and since there is at least one element in rel that contains AAB, the qualification is always true! (i.e., this is an existential query). hence, "Y" is retrieved in place of every rel.a... -- Paul M. Aoki | CS Div., Dept. of EECS, UCB | aoki@postgres.Berkeley.EDU | Berkeley, CA 94720 | ...!uunet!ucbvax!aoki