#!/opt/perl-5.20/bin/perl
use strict;
use warnings;
use DBI;
main();
exit;
sub main {
  my $dbh = DBI->connect or die "oops - $!\n";
  my $Customer_ID = 10;
  my $sql = "select customer_id from t where customer_id = ?";
  my $sth = $dbh->prepare($sql)  or die "oops - $!\n";
  my $rc  = $sth->execute($Customer_ID);
  while (my $rrow = $sth->fetch) { print $rrow->[0], "\n"; }
}

##</code><code>##

$ DBI_TRACE=0 ./customer_dbi.pl
10


$ DBI_TRACE=1 ./customer_dbi.pl
    DBI 1.628-nothread default trace level set to 0x0/1 (pid 5340 pi 0) at DBI.pm line 287 via customer_dbi.pl line 4
    -> DBI->connect(, , ****)
    -> DBI->install_driver(Pg) for linux perl=5.020000 pid=5340 ruid=500 euid=500
       install_driver: DBD::Pg version 2.19.3 loaded from /home/aardvark/perl-5.20/lib/site_perl/5.20.0/x86_64-linux/DBD/Pg.pm
    <- install_driver= DBI::dr=HASH(0xd1ad40)
    !! warn: 0 CLEARED by call to default_user method
    <- default_user(undef, undef, ...)= ( undef undef ) [2 items] at DBI.pm line 657
    <- connect('', undef, ...)= ( DBI::db=HASH(0xfd4258) ) [1 items] at DBI.pm line 669
    <- STORE('PrintError', 1)= ( 1 ) [1 items] at DBI.pm line 721
    <- STORE('AutoCommit', 1)= ( 1 ) [1 items] at DBI.pm line 721
    <- STORE('Username', undef)= ( 1 ) [1 items] at DBI.pm line 724
    <- connected= ( undef ) [1 items] at DBI.pm line 731
    <- connect= DBI::db=HASH(0xfd4258)
    <- STORE('dbi_connect_closure', CODE(0xfd3c58))= ( 1 ) [1 items] at DBI.pm line 740
    <- prepare('select * from t where customer_id = ?')= ( DBI::st=HASH(0xfd4588) ) [1 items] at customer_dbi.pl line 12
    <- execute(10)= ( 1 ) [1 items] at customer_dbi.pl line 13
    <- fetch= ( [ 10 ] ) [1 items] row1 at customer_dbi.pl line 14
10
    <- fetch= ( undef ) [1 items] row1 at customer_dbi.pl line 14
    <- DESTROY(DBI::st=HASH(0xfd4348))= ( undef ) [1 items] at customer_dbi.pl line 5
    <- DESTROY(DBI::db=HASH(0xfd4198))= ( undef ) [1 items] at customer_dbi.pl line 5
    <- disconnect_all= ( '' ) [1 items] at DBI.pm line 748
!   <- DESTROY(DBI::dr=HASH(0xd1ad40))= ( undef ) [1 items] during global destruction