my @tabular  = $dbi->array_of_hashrefs_please();

    # move into a hash (keyed by category) of array of hashrefs (rows)
    my %categories;
	foreach( @tabular )
	{
        my $entry = $_->{ FIELD_I_WANT_TO_SORT_BY };
		if ( $categories{$entry} == undef )   
        { 
            $categories{$entry} = [$_] ;        
        }
		else                                  
        { 
            push @{$categories{$entry}}, $_;    
        }
	}

    # now create nested loop based on category...

	my @nested_loop;
	foreach(sort keys %categories)
	{
	   push @nested_loop, { category => $_, entries => $categories{$_}};
	}

    # add our nested loop to the template
	$template->param( my_loop => \@nested_loop);

##</code><code>##

    <tmpl_loop name="my_loop">
            <tmpl_var name="category">
            <tmpl_loop name="entries">
                <!-- inner loop data here -->
            </tmpl_loop>
    </tmpl_loop>