I'm actually surprised that you say your first approach works. It doesn't seem to work for me, unless the string being passed for the single placeholder happens to contain only one field value: 
my $in = "a,b";
my $sth = $dbh->prepare("SELECT foo FROM bar WHERE baz IN (?)");
$sth->execute( $in );

# fetch returns no results -- it would work if $in were just "a"


my @in = qw/a b/;
$sth = $dbh->prepare("SELECT foo FROM bar WHERE baz in (?,?)");
$sth->execute( @in );

# fetch returns expected results for "a" and "b"

[download]
(I'm using perl 5.8.6 on freebsd, with mysql 4.0.21)

Given that circumstance, I would definitely use the  join( ',', map {'?'} @ins approach for putting together the text for the sql select statement (like davidrw showed in his reply).

In reply to Re: DBI and variable numbers of bind parameters by graff
in thread DBI and variable numbers of bind parameters by friedo

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.