return this.ordering.equals(that.ordering);
    }
    return false;
  }

  @Override
  public int hashCode() {
    return ordering.hashCode() ^ 957692532; // meaningless
  }

  @Override
  public String toString() {
    return ordering + ".nullsFirst()";
  }

  private static final long serialVersionUID = 0;

// Row function - An expression that depends on a value in the
// row. They have an output for each input row.
//
// Some types of a queries are not valid. For example, an aggregation
// function combined with a row function is meaningless ("AVG(s.Age) +
// s.Salary"). Analysis determines if such a scenario exists so an
// error can be returned.

var (
	// Fatal error for query processing.

 *
 * <p>Use this class instead of direct calls to {@link System#nanoTime} for two reasons:
 *
 * <ul>
 *   <li>The raw {@code long} values returned by {@code nanoTime} are meaningless and unsafe to use
 *       in any other way than how {@code Stopwatch} uses them.
 *   <li>An alternative source of nanosecond ticks can be substituted, for example for testing or