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Re: PostgreSQL order of evaluation

From: marten(at)feki(dot)toppoint(dot)de
To: pgsql-general(at)hub(dot)org
Subject: Re: PostgreSQL order of evaluation
Date: 1999-08-22 16:23:56
Message-ID: 199908221623.JAA09740@feki.toppoint.de (view raw or flat)
Thread:
Lists: pgsql-general
> 
> Date: Fri, 20 Aug 1999 01:25:54 +0200
> From: Petter Reinholdtsen <pere(at)hungry(dot)com>
> Subject: PostgreSQL order of evaluation
> 
> I've been trying to find where the order of evaluation for SQL is
> defined.  In short, I wounder if the following always gives the same
> result:
> 
>         CREATE SEQUENCE counter
>                 start 1 increment 1 cache 1
>                         minvalue 1
>                         maxvalue 2147483647;
>         SELECT NEXTVAL('counter'), NEXTVAL('counter');
> 
>         CREATE TABLE counts (
>                value1 integer,
>                value2 integer
>         );
>         INSERT INTO counts VALUES (NEXTVAL('counter'), NEXTVAL('counter'));
> 
> Will the first always return (1, 2) or are the SQL implementations
> free to return (2,1).  Will every SQL implementation insert (3,4) in
> the table, or will some insert (4,3).
> 

 Why are you so sure, that you may get numbers with differences of
one ? As I understand the backend caches several numbers in advance
and when running several backends you may also get numbers like
(1,10).

 After all: the only thing you can be sure: both numbers are unique !

 Marten


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