I always use something like the following to check for existance of things in a database table, by selecting count(*) of rows that match. If count is 0 then the user does not exist. This method is portable. Note that I also used placeholders in the SQL, which is recommended for security reasons.
# return 1 (true) if user is found, 0 (false) if not found
sub check_exist {
  $username = shift;

  # do the necessary dbi conection...

  $sql = qq{SELECT count(*) FROM members WHERE nick=?};
  $sth = $dbh->prepare($sql);
  $sth->execute($username) or bail_out("Can not execute SQL query");
  my ($rowcount) = $sth->fetchrow();
  $dbh->disconnect();

  return $rowcount > 0;
}

[download]
Then your main code would look something like:
if (check_exist($user)) {
   # handle_exception...
} else {
   # user does not exist
}

[download]

In reply to Re: perl (mysql) question... by Roger
in thread perl (mysql) question... by kiat

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.