To: pgsql-sql@postgresql.org
From: Jasen Betts <jasen@xnet.co.nz>
Subject: Re: Generic design: char vs varchar primary keys
Date: 5 Aug 2011 12:40:19 GMT
Organization: Dis (not Dat) Organisation
Lines: 29
Message-ID: <j1gobj$m5j$1@reversiblemaps.ath.cx>
References: <201108032040.17628.raju@linux-delhi.org>
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On 2011-08-03, Raj Mathur (=?utf-8?b?4KSw4KS+4KSc?= =?utf-8?b?IOCkruCkvuCkpeClgeCksA==?=) <raju@linux-delhi.org> wrote:
> Hi,
>
> Can you point me to any pages that explain the difference between using, 
> say CHAR(8) vs VARCHAR(8) as the primary key for a table?  Is there any 
> impact on the database in terms of:

look in the data types chapter of the manual

> - Speed of indexed retrieval
> - Speed of join from a referencing table
> - Storage (I presume VARHAR(8) would have a slight edge, in general)
> - Any other issue

Unless you need the padding, and/or the length constraints use text.

("usr/share/doc/postgresql-doc-8.4/html/datatype-character.html")

.     Tip:  There is no performance difference among these three types,
. apart from increased storage space when using the blank-padded type,
. and a few extra CPU cycles to check the length when storing into a
. length-constrained column. While character(n) has performance
. advantages in some other database systems, there is no such advantage
. in PostgreSQL; in fact character(n) is usually the slowest of the
. three because of its additional storage costs. In most situations text
. or character varying should be used instead. 

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