code: func (p *PhysicalIndexReader) ResolveIndices() (err error) {
  	err = p.physicalSchemaProducer.ResolveIndices()
  	if err != nil {
  		return err
  	}
  	err = p.indexPlan.ResolveIndices()
  	if err != nil {
  		return err
  	}
  	for i, col := range p.OutputColumns {
  		newCol, err := col.ResolveIndices(p.indexPlan.Schema())
  		if err != nil {
  			return err
  		}
  		p.OutputColumns[i] = newCol.(*expression.Column)
  	}
  	return
  }
docs: // ResolveIndices implements Plan interface.