compare_rows_if_equal_keys are comparison functions used to compare rows in a table in order to sort them.
compare_keys compares two rows based on a single column in the table's sort criteria.
compare_rows_if_equal_keys compares two rows based on their row ids, and is only called if the calls to
compare_key for all columns in the table's sort criteria return 0. The sort direction is determined by the first column in the sort criteria.
val compare_rows_if_equal_keys : cmp_row_id:( 'row_id -> 'row_id -> int ) -> Sort_dir.t -> 'row_id -> 'row_id -> int