code: func (p *basePhysicalAgg) ResolveIndices() (err error) {
  	err = p.physicalSchemaProducer.ResolveIndices()
  	if err != nil {
  		return err
  	}
  	for _, aggFun := range p.AggFuncs {
  		for i, arg := range aggFun.Args {
  			aggFun.Args[i], err = arg.ResolveIndices(p.children[0].Schema())
  			if err != nil {
  				return err
  			}
  		}
  	}
  	for i, item := range p.GroupByItems {
  		p.GroupByItems[i], err = item.ResolveIndices(p.children[0].Schema())
  		if err != nil {
  			return err
  		}
  	}
  	return
  }
docs: // ResolveIndices implements Plan interface.