code: func (visitor *toStringVisitor) VisitFieldExpression(exp *sql.FieldExpression) {
  	if visitor.entity == nil {
  		visitor.lastError = ErrMissingVisitorEntity
  	} else {
  		field, found := structs.FindField(exp.PointerToAField, visitor.entity)
  		if !found {
  			visitor.lastError = ErrMissingEntityField
  			return
  		}
  		fieldName, found := fieldName(field)
  		if !found {
  			visitor.lastError = ErrUnexportedEntityField
  			return
  		}
  		//visitor.generated.WriteString(" ")
  		visitor.generated.WriteString(fieldName)
  
  		if exp.AfterField != nil {
  			exp.AfterField.Accept(visitor)
  		}
  	}
  }
docs: // VisitPrefixedExp generates part of SQL expression