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			# Fast path: no join-key alias to exclude and no collision renames
			@merged{keys %{$s}} = values %{$s};
		} else {
			for my $col (keys %{$s}) {
				next if $skip_jc && $col eq $local_jc;
				$merged{ $renames->{$col} // $col } = $s->{$col};
			}
		}
	}

	delete @merged{keys %{ $self->{_removed_cols} }}
		if %{ $self->{_removed_cols} };

	$self->{_schema_cache} = \%merged;
	return $self->{_schema_cache};
}

=head2 updated

=head3 SYNOPSIS

    my $ts = $join->updated();

=head3 DESCRIPTION

Returns the Unix timestamp of the most recent modification across all
component databases.  This is the maximum of all individual C<updated()>
return values.

Use this to implement simple cache-invalidation logic: if C<updated()>
has advanced since your last snapshot, re-query.

=head3 API SPECIFICATION

=head4 Input

    None.

=head4 Output

    Unix timestamp (positive integer).

=head3 EXAMPLE

    my $last_modified = $join->updated();
    if ($last_modified > $my_cache_timestamp) {
        $my_cache = $join->selectall_arrayref();
        $my_cache_timestamp = $last_modified;
    }

=head3 MESSAGES

C<updated()> does not emit any warnings or errors.  Component databases that do
not implement C<updated()>, or whose C<updated()> throws, are silently skipped;
only defined return values contribute to the maximum.  If no component database
implements C<updated()>, C<undef> is returned (same as C<List::Util::max> on an
empty list).

=cut

sub updated {
	my ($self) = @_;
	my @timestamps;
	for my $db (@{ $self->{_dbs} }) {
		my $ts;
		do { local $@; $ts = eval { $db->updated() } };
		push @timestamps, $ts if defined $ts;
	}
	return max(@timestamps);
}

=head2 set_logger

=head3 SYNOPSIS

    $join->set_logger($log);
    $join->set_logger(logger => $log);   # named-pair form also accepted

=head3 DESCRIPTION

Attaches a new logger object to the join and propagates it to every component
database.  The logger is used for diagnostic output by all component databases.

Non-blessed values (a log-level string such as C<"debug">, a filename, or a
code reference) are wrapped in C<Log::Abstraction->new(...)> automatically,
matching the behaviour of C<Database::Abstraction::set_logger>.

=head3 API SPECIFICATION

=head4 Input

    logger  Positional or named: a logger object, log-level string, filename,
            or code reference (required).  Non-blessed values are wrapped in
            Log::Abstraction automatically.

=head4 Output

    Returns C<$self> for method chaining.

=head3 EXAMPLE

    # Log::Any is used here as an example; any object that implements
    # debug() and info() (or whichever methods your component databases
    # call internally) works equally well.
    use Log::Any qw($log);

    my $join = Database::Join->new(databases => [$db1, $db2], join_column => 'entry');
    $join->set_logger($log);
    # $log is now used by $join and by $db1 and $db2

    # Named-pair form (mirrors Database::Abstraction API):
    $join->set_logger(logger => $log);

=head3 MESSAGES

    (croak) Usage: set_logger(logger => $logger)
        -- Called with an undefined argument.  Pass a valid logger object.

=cut

sub set_logger {