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Re: doubt about datum

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Luca Ferrari <fluca1978(at)infinito(dot)it>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: doubt about datum
Date: 2007-07-31 05:40:03
Message-ID: 7021.1185860403@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-novice
Luca Ferrari <fluca1978(at)infinito(dot)it> writes:
> I'm new to postgresql programming and I'd like to understand what a datum is 

A value of any data type -- which particular type is not said by the
datum itself, but we always have context information to tell us that.

> Moreover why it does not need transaction 
> visibility as an ordinary tuple (xmin, cmin, cmax, xmax)?

Datums are values.  '42'::int does not need visibility information;
its value is always the same.

			regards, tom lane

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