code: func (p *Update) ResolveIndices() (err error) {
  	err = p.baseSchemaProducer.ResolveIndices()
  	if err != nil {
  		return err
  	}
  	schema := p.SelectPlan.Schema()
  	for _, assign := range p.OrderedList {
  		newCol, err := assign.Col.ResolveIndices(schema)
  		if err != nil {
  			return err
  		}
  		assign.Col = newCol.(*expression.Column)
  		assign.Expr, err = assign.Expr.ResolveIndices(schema)
  		if err != nil {
  			return err
  		}
  	}
  	return
  }
docs: // ResolveIndices implements Plan interface.