Re: newbie: Column CHECK(col contains '@') ? - Mailing list pgsql-novice

Wow... and this is the Novice list?  Thanks Andrew, you cover it all from a to z.  It'll take me a bit of work to
digestyour message and put it into practice, as the (weird and) wonderful world of regex's is very new to me.  

regards
/j-p.


On 13 May 2002, Andrew McMillan wrote:

> On Mon, 2002-05-13 at 11:21, john-paul delaney wrote:
> > Thanks Joel... that did the trick (even better than I had asked for).
> > Forgive my ignorance, but it your solution a regular expression?
> >
> > Can anyone suggest a good source where I can read up on these (regex's)
> > in relation to postgresql?
>
> The PostgreSQL manual has a section (section 4.6) on pattern matching
> using REGEX and pattern matching using the SQL 'LIKE' operator.
>
> The LIKE operator (which was what Joel used in his solution for you)
> uses '%' as a wildcard and _ as a single character match.
>
> Regex is much more complicated, and there are many sources of help for
> it out on the internet.  A similar check using a regex operator would be
> something like:
>
> (em ~ '@.*\.')
>
> since there is no need to specify leading and trailing wildcards within
> a regex (instead you specify that you want to anchor the regex to the
> beginning and/or ending of the string).
>
> A search on the internet might provide a more thorough regex for
> validation of e-mail addresses.  A slightly more complex one I have used
> is:
>
> (em ~* '^[^@]+@[a-z0-9-]+\.[a-z]+')
>
> which should validate (a) there is only a single '@' in the address and
> (b) the first part of the domain name contains only valid domain-name
> like characters.  The ~* operator is the case insensitive regex match
> which I didn't use in the one above since there was no alphabetic
> matching involved.
>
> How I do this in my own applications is actually to implement a function
> for valid email addresses, viz:
>
> CREATE FUNCTION valid_email(TEXT) RETURNS BOOLEAN AS '
>   DECLARE
>     email ALIAS FOR $1;
>     user TEXT;
>     domain TEXT;
>   BEGIN
>     IF email !~ ''.@.'' THEN
>       RETURN FALSE; -- One @ good
>     END IF;
>     IF email ~ ''@.*@'' THEN
>       RETURN FALSE; -- Two @s bad
>     END IF;
>     domain := substring( email from position( ''@'' in email) + 1 );
>     user   := substring( email from 1 for position( ''@'' in email) - 1
> );
>     IF domain ~* ''([a-z0-9-]+\.)+([a-z])?[a-z][a-z]$'' THEN
>       -- Only really worth validating the domain
>       RETURN TRUE;
>     END IF;
>     RETURN FALSE;
>   END;
> ' LANGUAGE 'plpgsql';
>
> This checks for internal spaces as well, and means that the rules for
> valid e-mail addresses happens in only one place.
>
> Regards,
>                     Andrew.
> >
> > thanks again,
> > /j-p.
> >
> >
> > On Sun, 12 May 2002, Joel Burton wrote:
> >
> > > > One column in my table contains email addresses - I want to check
> > > > that any value entered contains a '@'.  How do I create a
> > > > CONSTRAINT or CHECK to ensure this when creating the table?
> > >
> > > create table em (
> > >   em text constraint is_email check (em like '%@%.%')
> > > );
> > >
> > > will work fine, assuming that this check (something @ something . something)
> > > is acceptable in your context as "looks like an email address"
> > >
> > > - J.
> > >
> > > Joel BURTON | joel@joelburton.com | joelburton.com | aim: wjoelburton
> > > Knowledge Management & Technology Consultant
> > >
> >
> >
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> >
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