code: func (p *LogicalTableDual) DeriveStats(childStats []*property.StatsInfo) (*property.StatsInfo, error) {
  	profile := &property.StatsInfo{
  		RowCount:    float64(p.RowCount),
  		Cardinality: make([]float64, p.Schema().Len()),
  	}
  	for i := range profile.Cardinality {
  		profile.Cardinality[i] = float64(p.RowCount)
  	}
  	p.stats = profile
  	return p.stats, nil
  }
docs: // DeriveStats implement LogicalPlan DeriveStats interface.