One thing that I do is put the reporting queries for my tables into their respective CDBI classes for organizational purposes. It helps keep all the related queries together. Then I make a method in the class that runs the query and returns the result. Here's a small example:

# in package DB::Contribition

__PACKAGE__->set_sql(average_dollars => <<'END_SQL' );
SELECT AVG(amount)
FROM   contribution
END_SQL

sub average_dollars {
    my $class = shift;
    my $sth  = $class->sql_average_dollars();
    $sth->execute();
    return $sth->select_val() || 0;
}
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