package SQL_functions;

sub select_picture_from_userID{
  my $userID = shift;
  "SELECT pict FROM users WHERE ID = $userID;"
}

sub select_some_nifty_case_with_contstraints{
  ... #hehe, perl6 only
}

#and in the "main" code:
use SQL_functions qw/:all/;
my $sth = $dbh->prepare( select_picture_from_userID( 666 ) ) or die...