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=cut

sub execute
{
	my $self = shift;

	if($self->{'berkeley'}) {
		Carp::croak(ref($self), ': execute is meaningless on a NoSQL database');
	}

	my $args = Params::Get::get_params('query', @_);

	# Ensure the 'query' parameter is provided
	Carp::croak(__PACKAGE__, ': Usage: execute(query => $query)')
		unless defined $args->{'query'};

	my $table = $self->_open_table($args);

	my $query = $args->{'query'};

	# Append "FROM <table>" if missing
	$query .= " FROM $table" unless $query =~ /\sFROM\s/i;

	# Log the query if a logger is available
	$self->_debug("execute $query");

	# Prepare and execute the query
	my $sth = $self->{$table}->prepare_cached($query);
	# DBI->execute() takes a list; normalise args to an array whether it
	# was passed as an arrayref ([30]) or a bare scalar/list (30).
	if(exists($args->{'args'})) {
		my @bind = ref($args->{'args'}) eq 'ARRAY' ? @{$args->{'args'}} : ($args->{'args'});
		$sth->execute(@bind) or croak("$query: ", join(', ', @bind));
	} else {
		$sth->execute() or croak($query);
	}

	# Fetch the results
	my @results;
	while (my $row = $sth->fetchrow_hashref()) {
		unless(wantarray) {
			$sth->finish();
			return $row;
		}
		push @results, $row;
	}

	# Return all rows as an array in list context
	return @results;
}

=head2 updated

Returns the Unix timestamp of the last database update (mtime for
file-based backends, or the time of the most recent C<new()> call for
DSN-based connections).

=cut

sub updated {
	my $self = shift;

	return $self->{'_updated'};
}

=head2 columns

Returns an array reference of column names for the current table.

    my $cols = $db->columns();    # e.g. ['entry', 'name', 'score', 'status']

The column list is determined by the backend:

=over 4

=item * B<Slurp mode> - sorted keys of the first row in memory.

=item * B<SQLite / other DBI> - a zero-row C<SELECT *> exposes the driver's
C<NAME> attribute.

=item * B<BerkeleyDB> - always returns C<['entry', 'value']>.

=back

The result is cached inside the object after the first call.

=cut

sub columns {
	my $self = shift;

	return $self->{'_columns'} if $self->{'_columns'};

	my $table = $self->_open_table({});

	my @cols;

	if($self->{'berkeley'}) {
		return $self->{'_columns'} = ['entry', 'value'];
	}

	if(my $data = $self->{'data'}) {
		if(ref($data) eq 'HASH') {
			my ($first) = values %{$data};
			@cols = sort keys %{$first} if $first;
		}
	} else {
		my $sth = $self->{$table}->prepare_cached("SELECT * FROM $table WHERE 1=0");
		$sth->execute();
		@cols = @{$sth->{NAME}};
		$sth->finish();
	}

	return $self->{'_columns'} = \@cols;
}

=head2 schema

Returns a hash reference describing the schema of the current table.
Each key is a column name; each value is a hash reference with these keys: