PHP，如何扩展我的代码以检查给定位置是否未包含在数据库中？

Question

从现有位置获取数据效果很好，但不检查错误。class Information extends DB {function get(){$loc=$_GET['loc'];  return $this->select("SELECT location, MAX(population), MAX(total_deaths_per_million),  MAX(total_cases), MAX(total_deaths), MAX(total_cases_per_million) FROM corona WHERE location= '$loc'");}}

Answer 1

可以先查询位置。我还没有运行它来测试它，但是像这样的东西应该可以解决问题

class Information extends DB {

function get(){

$loc=$_GET['loc'];    

$locationResults = $this->select("SELECT location FROM corona WHERE location= '$loc'");

if ($locationResults->num_rows == 0) {

    echo "If the number of rows returned is equal to 0, then there's no locations for the location the user gave";      

    } else {

       return $this->select("SELECT location, MAX(population), MAX(total_deaths_per_million),  MAX(total_cases), MAX(total_deaths), MAX(total_cases_per_million) FROM corona WHERE location= '$loc'");

    }// end else

  }//end function

}//end class