Date: Sat, 8 Jul 2006 05:54:03 -0600
From: Michael Fuhr <mike@fuhr.org>
To: Richard Broersma Jr <rabroersma@yahoo.com>
Cc: SQL Postgresql List <pgsql-sql@postgresql.org>
Subject: Re: Celko's Puzzle Number 5
Message-ID: <20060708115403.GA13518@winnie.fuhr.org>
References: <20060708063457.56830.qmail@web31810.mail.mud.yahoo.com>
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On Fri, Jul 07, 2006 at 11:34:57PM -0700, Richard Broersma Jr wrote:
> "How do you ensure that a column will have a single alphabetic
> character string in it? (That means no spaces, no numbers, and
> no special characters.)"

You can check patterns with regular expressions.  PostgreSQL supports
SIMILAR TO, which is standard SQL since SQL:1999, and POSIX regular
expressions; see "Pattern Matching" in the "Functions and Operators"
chapter of the documentation:

http://www.postgresql.org/docs/8.1/interactive/functions-matching.html

Any of these CHECK expressions should work:

  CHECK (alpha_only SIMILAR TO '[A-Za-z]+')
  CHECK (alpha_only ~ '^[A-Za-z]+$')
  CHECK (alpha_only ~* '^[a-z]+$')

Unfortunately, even though SIMILAR TO has been standard SQL for
several years, not all databases implement it.  Many databases
do support regular expressions but generally via a non-standard
syntax (as PostgreSQL does with its ~, ~*, !*, and !~*  operators).

-- 
Michael Fuhr