sybperl-l Archive

From: Michael Peppler <mpeppler at peppler dot org>
Subject: Re: Different result from convert(varchar(255), a) and convert(a)
Date: Nov 24 2003 6:03PM

On Mon, 2003-11-24 at 09:18, Avis, Ed wrote:
> When selecting a 'real' column you get a different string value in
> Perl from 'select convert(varchar(255), a)' and 'select a':
> 
>     $dbh->{AutoCommit} = 1;
>     $dbh->do('create table #a (a real not null)');
>     $dbh->do('insert into #a (a) values (.51645678281784058)');
>     my $sql = "select convert(varchar(255), a), a from #a";
>     my $sth = $dbh->prepare($sql);
>     $sth->execute();
>     while (my @r = $sth->fetchrow_array()) {
>         print "@r\n";
>     }
>     disconnect $dbh;
> 
> This prints, on my system:
> 
> .51645678281784058 0.516456782817841
> 
> The trailing zero doesn't matter but the loss of precision is bad.  I
> know that 'real' is an approximate numeric type in Sybase but here
> Perl is giving me less precision than Sybase offers.

DBD::Sybase actually simply retrieves the REAL/FLOAT data item in native
format and stores it in the perl variable as number - it never is
converted to a char string until you print it out.

The rounding that you are seeing is probably happening in perl's print
statement:

while (my @r = $sth->fetchrow_array()) {        
    printf "%s %.20f\n", @r;    
}

gives me:

.51645678281784058 0.51645678281784057617

Of course all of these digits are approximations, so I don't think you
should make a big deal out of this...

Michael
-- 
Michael Peppler                              Data Migrations, Inc.
mpeppler@peppler.org                 http://www.mbay.net/~mpeppler
Sybase T-SQL/OpenClient/OpenServer/C/Perl developer available for short or 
long term contract positions - http://www.mbay.net/~mpeppler/resume.html