use strict;

my @views = ( 'view0', 'view1', 'view2', 'view3' );

my %columns = ( 'view0' => [qw(buffersize size value)],
                'view1' => [qw(buffersize size value)],
                'view2' => [qw(buffersize size value)],
                'view3' => [qw(buffersize size value)] );

print build_query(\@views, \%columns), "\n";

my $last;

sub build_query {
    my($views, $columns) = @_;

    my $first = shift @{$views};
    $last = $first;
    return join(' full outer join ', $first,
                view_on_clauses($views, $columns));
}

sub view_on_clauses {
    my($views, $columns) = @_;
    return map { join(' ', $_, 'on', and_clause($_, $columns)) } @{$views};
}

sub and_clause {
    my($view, $columns) = @_;
    return join(' and ', equality_clauses($view, $columns));
}

sub equality_clauses {
    my($view, $columns) = @_;

    my @equality_clauses = ( );

    # Convert map into explicit for loop because we need to
    # merge together two different arrays. If the column names
    # are always the same, then map can be used.

    for (my $i = 0; $i < @{$columns->{$view}} - 1; ++$i) {
        push @equality_clauses,
             $last . '.' . $columns->{$last}[$i] . '=' .
             $view . '.' . $columns->{$view}[$i];
    }

    $last = $view;
    return @equality_clauses;
}