I'm trying to create a database search function, giving users the ability to select which fields to search for and which fields to return. In my examples, @q_return is columns to be returned, the keys from %q_search are the columns to be searched, @q_names contains the data to search for. The code below works, however, it's directly interpolating variables into the SQL search string 
my $query2 = "SELECT " . join(",", @q_return) . " FROM rma_list WHERE 
+(" . join(",", (keys %q_search)) . ") = (" . join(",", @q_names) . ")
+";
my $sth = $dbh->prepare($query2) or die "Couldn't prepare query: " . $
+dbh->errstr;
$sth->execute();

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I've modified this code to the following, to allow for placeholders with unknown count using map(). This search no longer returns any rows, with the same data as above. It doesn't die however, so I assume I'm matching the correct amount of variables. What could I be doing wrong here? 
my $query = "SELECT " . join(",", map { "?" } @q_return) . " FROM rma_
+list WHERE (" . join(",", map { "?" } (keys %q_search)) . ") = (" . j
+oin(",", map { "?" } @q_names) . ")";
my $sth = $dbh->prepare($query) or die "Couldn't prepare query: " . $d
+bh->errstr;
$sth->execute(@q_return, (keys %q_search), @q_names) or die "Could not
+ perform query: " . $sth->errstr;

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The outpuut from DBI's trace() shows me the following, but I'm unfortunately a little inexperienced to understand it. 
     DBI::db=HASH(0x1b76164) trace level set to 0x0/2 (DBI @ 0x0/0) in
+ DBI 1.607-ithread (pid 3392), referer: http://localhost/cgi-bin/temp
+.cgi
     -> prepare for DBD::mysql::db (DBI::db=HASH(0x1b761a4)~0x1b76164 
+'SELECT ?,?,?,?,? FROM rma_list WHERE (?) = (?)') thr#233e34, referer
+: http://localhost/cgi-bin/temp.cgi
 \t-> dbd_st_prepare MYSQL_VERSION_ID 50013, referer: http://localhost
+/cgi-bin/temp.cgi
 \t>- dbd_st_free_result_sets, referer: http://localhost/cgi-bin/temp.
+cgi
 \t<- dbd_st_free_result_sets RC -1, referer: http://localhost/cgi-bin
+/temp.cgi
 \t<- dbd_st_free_result_sets, referer: http://localhost/cgi-bin/temp.
+cgi
 \t<- dbd_st_prepare, referer: http://localhost/cgi-bin/temp.cgi
     <- prepare= DBI::st=HASH(0x16ce66c) at temp.cgi line 273, referer
+: http://localhost/cgi-bin/temp.cgi
     -> execute for DBD::mysql::st (DBI::st=HASH(0x16ce66c)~0x1bd12cc 
+'status' 'rma_num' 'auth_id' 'vendor' 'part_num' 'status' '0') thr#23
+3e34, referer: http://localhost/cgi-bin/temp.cgi
  -> dbd_st_execute for 01b875f4, referer: http://localhost/cgi-bin/te
+mp.cgi
 \t>- dbd_st_free_result_sets, referer: http://localhost/cgi-bin/temp.
+cgi
 \t<- dbd_st_free_result_sets RC -1, referer: http://localhost/cgi-bin
+/temp.cgi
 \t<- dbd_st_free_result_sets, referer: http://localhost/cgi-bin/temp.
+cgi
 mysql_st_internal_execute MYSQL_VERSION_ID 50013, referer: http://loc
+alhost/cgi-bin/temp.cgi
 Binding parameters: SELECT 'status','rma_num','auth_id','vendor','par
+t_num' FROM rma_list WHERE ('status') = ('0'), referer: http://localh
+ost/cgi-bin/temp.cgi
  <- dbd_st_execute returning imp_sth->row_num 0, referer: http://loca
+lhost/cgi-bin/temp.cgi
     <- execute= '0E0' at temp.cgi line 274, referer: http://localhost
+/cgi-bin/temp.cgi
     -> trace for DBD::mysql::db (DBI::db=HASH(0x1b761a4)~0x1b76164 0)
+ thr#233e34, referer: http://localhost/cgi-bin/temp.cgi
     <- trace= ( 2 ) [1 items] at temp.cgi line 275, referer: http://l
+ocalhost/cgi-bin/temp.cgi
 [Tue Aug 18 18:35:26 2009] temp.cgi: 2 at C:/Documents and Settings/A
+dministrator/My Documents/RMA Beta/cgi-bin/temp.cgi line 275., refere
+r: http://localhost/cgi-bin/temp.cgi
     -> DESTROY for DBD::mysql::st (DBI::st=HASH(0x1bd12cc)~INNER) thr
+#233e34, referer: http://localhost/cgi-bin/temp.cgi
 , referer: http://localhost/cgi-bin/temp.cgi
 --> dbd_st_finish, referer: http://localhost/cgi-bin/temp.cgi
 \t>- dbd_st_free_result_sets, referer: http://localhost/cgi-bin/temp.
+cgi
 \t<- dbd_st_free_result_sets RC -1, referer: http://localhost/cgi-bin
+/temp.cgi
 \t<- dbd_st_free_result_sets, referer: http://localhost/cgi-bin/temp.
+cgi
 , referer: http://localhost/cgi-bin/temp.cgi
 <-- dbd_st_finish, referer: http://localhost/cgi-bin/temp.cgi
 \tFreeing 7 parameters, bind 0 fbind 0, referer: http://localhost/cgi
+-bin/temp.cgi
     <- DESTROY= undef at Carp.pm line 356, referer: http://localhost/
+cgi-bin/temp.cgi

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Also, I've made an effort to follow etiquette. I hope none of this is out of line. The code is likely ghastly, as I'm still learning the finer details of DBI.

In reply to Perl Mysql DBI, using placeholders with unknown variable count by Haioken

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