# "RaiseError => 1" tells DBI to die on errors.
my $dbh = DBI->connect($DSN, $username, $password, { RaiseError => 1 });

my $sth;

$sth = $dbh->prepare("
          SELECT table_name, column_name
          FROM Dba_tab_columns
          WHERE owner = ?
          ORDER BY table_name, column_name
        ");

$sth->execute($schema);

my $table_column = $sth->fetchall_arrayref;

$sth->finish;
        
for my $tcr (@{$table_column}) {
  if ($tcr->[0] eq "EMP") {
    my $sth = $dbh->prepare("SELECT " . $tcr->[1] . " FROM " . $schema . $tcr->[0]);
    $sth->execute;

    my $column_data = $sth->fetchall_arrayref;
    $sth->finish;
                
    # This for-loop create a hash of a hash of an array with the keys {table name} and {column name}
    for my $row (@{$column_data}) {
      push @{ $tables{$tcr->[0]}{$tcr->[1]} }, $row->[0];                   
    }
  }
}