Re: Celko's Puzzle Number 5

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