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    <p>As others have mentioned:</p> <pre><code>use strict; use warnings; </code></pre> <p>Also, every time you do a DBI call, you should be doing this:</p> <pre><code>if ($sth-&gt;err()) { die "ERROR: " . $sth-&gt;errstr() . "\n"; } </code></pre> <p>Even after a fetch. This will catch lots of the issues you might have.</p> <p>I simplified your program a wee bit:</p> <pre><code>use strict; use warnings; use DBI; my $connect = DBI-&gt;connect("$connectString", "$user", "$id"); if (not $connect) { die qq(connection error\n); } my $table = "session"; my $uniqueSessions = "SELECT DISTINCT SESSION FROM $table"; print qq(\$uniqueSessions = "$uniqueSessions"\n); my $queryUniques = $connect-&gt;prepare($uniqueSessions); if ($queryUniques-&gt;err()) { die "ERROR: " . $queryUniques-&gt;errstr() . "\n"; } $queryUniques-&gt;execute(); if ($queryUniques-&gt;err()) { die "ERROR: " . $queryUniques-&gt;errstr() . "\n"; } my $session; $queryUniques-&gt;bind_columns(\$session); my $counter = 1; my $sessionString; while(my $hashref = $queryUniques-&gt;fetch()) { print "Fetching Row\n"; if($counter == 1) { $sessionString = "'" . $session . "'"; } else { $sessionString = $sessionString . ", '" . $session . "'"; } $counter++; } if ($queryUniques-&gt;err()) { print "ERROR = " . $queryUniques-&gt;errstr . "\n"; } print "$sessionString\n"; </code></pre> <p>I basically took out the second query and fixed a few things here and there. The last line prints out the <code>$sessionString</code> which is a quote separated list of all of your sessions. This part worked.</p> <p>The second part is where things get weird. You are taking <code>$sessionString</code> and passing it as a SQL statement. Unless there's something I am not seeing, <code>$sessionString</code> is simply a list of sessions and not a SQL statement in itself.</p> <p>As I said, check for errors with each DBI call, and see if you're erroring out somewhere.</p> <p>You can also add a line like this:</p> <pre><code>print qq(DEBUG: SQL Query = '$sqlStatement'\n); </code></pre> <p>before you run a <code>$sth-&gt;prepare($sqlStatement)</code> and that way, you can see what your SQL statement is.</p> <hr> <h1>The Problem</h1> <p>It looks like you're preparing the second query before you figure out what <code>(?)</code> should be (which I assume is your group of $sessionString).</p> <p>You need to substitute the sessions with the <code>(?)</code> <strong>BEFORE</strong> you do your DBI->prepare().</p> <p>Something like this (<em>not tested</em>):</p> <pre><code>(my $sessionQuery = $query) =~ s/\(\?\)/$sessionString/; my $querySth = $connect-&gt;prepare($sessionQuery); $querySth-&gt;execute(); my @test = $queryPrep-&gt;fetchall_arrayref(); </code></pre> <p>Remember that <code>qq()</code> quoting syntax is your friend. I use this a lot:</p> <pre><code>print qq(DEBUG: \$foo = "$foo"\n); </code></pre> <p>And sometimes, I simply copy and paste a statement and then quote it:</p> <pre><code>print qq(DEBUG: while (my $foo = foobar($bar)) };\n); </code></pre> <p>It's amazing how many errors I can catch that way. I can then search for <code>DEBUG:</code> in my program and delete those lines.</p> <p>Remember write your programs a bit at a time, see if you can get <code>$sessionString</code> working. Then try to see if you can substitute that into your <code>$query</code>, then try executing the calculated query.</p> <p>Perl is a nice and powerful language, but the syntax can be a bit crufty at times -- especially if you're not use to object oriented Perl.</p>
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