foreach $tbl1_primary (keys(%$table1)) {
 foreach (keys(%$table3)) {
  while ( $table3->{$_}{$table1->{$tbl1_primary}{foreign_key}} == 
$table3->{$_}{foreign_key} ) {
  $table1_foreign_key_table3 = 
   $table3->{$_}{$table1->{$tbl1_primary}{foreign_key}};
  }
 }
}