As tantarbobus as mentioned already, you can't have a count of rows beforehand with MySQL, unless you make sure you are using mysql_store_result (which is the default mode with DBD::mysql, BTW).

In PHP it's the same story. PHP is hiding complexity from you. If the method mysql_num_rows() works, it's only because PHP uses always mysql_store_result(). If you read the relevant explanation on MySQL manual you'll see that a count of rows is only possible after you are finished fetching them.

That said, If you want to be sure of the row number and you don't want to use a separate COUNT(*), then the only way is to use one of the "fetchall_*" or "selectall_*" methods from the DBI.

my $sth = $dbh->prepare($sql);
$sth->execute || $error->LogError("whatever ".$dbh->errstr, 0);
my $recs = $sth->fetchall_arrayref;
my $count = @$recs;

[download]

Once you have the records stored in an array, the number of records is given, as for any array in Perl, testing the array in scalar context.

In reply to Re: DBI, From PHP to Perl by dbwiz
in thread DBI, From PHP to Perl by dstefani

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.