将MySQL结果存储在PHP数组中以进行两个查询

Question

How do I create, store and output an array that uses two different mysql queries?

I tried to make a simple example.

$select1 = "SELECT country_id, country_name FROM countries ...";
while ($select1) {
   ...store country results in array...

  $select2 = "SELECT city_id, city_name FROM cities where '" . $select1['country_id'] . "'..."); // depends on select1
  while ($select2) {
    ...store city results in array...
  }

}

**output something like this:**

country_id = 1
country_name = United States

  city_id = 1
  city_name = New York

  city_id = 2
  city_name = Las Vegas

country_id = 2
country_name = Canada

  city_id = 3
  city_name = Ottawa

Answer 1

I do not know if you are checking for errors, preparing or escaping your queries but please do so.

To generate your array you can do it with this:

    $list = [];
    $countries = $link->query("SELECT country_id, country_name FROM countries ...");

    while ($country_row /*fetch from $countries*/) {

        $country_id = $country_row['country_id']; 

        $country_info = [
                'country_id' => $country_id,
                'country_name' => $country_row['country_name'],
                'country_cities' => []
         ];

        $cities_stmt = "SELECT city_id, city_name FROM cities where $country_id...";
        $cities = $link->query($cities_stmt);

        while ($city_row /*fetch from $cities*/) {

            $city_id = $city_row['city_id'];

            $country_info['country_cities'][$city_id] = [
                    'city_id' => $city_id,
                    'city_name' => $city_row['city_name']
            ];
        }

        $list[$country_id] = $country_info;
    }

To display your array you can do:

    foreach ( $list as $country_id => $country_info ) {

        echo "Country ID: $country_id<br />";
        echo 'Country Name: ' . $country_info['country_name'] . '<br />';
        echo 'Country Cities:<br />';

        $cities = $country_info['country_cities']; 

        foreach ( $cities as $city_id => $city_info ) {

                echo "   City ID: $city_id<br />";
                echo '   City Name: ' . $city_info['city_name'] . '<br />';
        }

        echo '<br />';
    }

Also, if you know the country id or city id you can do:

    echo 'City Name: ' . $list[$country_id]['country_cities'][$city_id]['city_name'] . '<br />';

Answer 2

Use your country_id as the key for your array.. So basically,

$select1 = mysqli_query("SELECT country_id, country_name FROM countries");
while ($country_row = mysqli_fetch_array($select1, MYSQLI_ASSOC)) {
   $array[$country_id]['country_id'] = $country_row ['country_id'];
   $array[$country_id]['country'] = $country_row['country_name'];

  $select2 = mysqli_query("SELECT city_id, city_name FROM cities where '" . $select1['country_id'] ."' "); // depends on select1
  while ($city_row = mysqli_fetch_array($select2, MYSQLI_ASSOC)) {
   $array[$country_id]['cities'][]['city_id'] = $city_row['city_id'];
   $array[$country_id]['cities'][]['city_name'] = $city_row['city_name']
  }
}

In order to print these back out using foreach (as you asked in comments), you must loop through both levels of the array

foreach($array as $country){
   //Loop through the countries that we queried and stored 
   echo 'Country Name: '.$country['country_name'].'<br/>';
   echo 'Country ID: '.$country['country_id'].'<br/>';
   echo 'Cities in country: <br/>';
   //Loop through the cities within this country
   foreach($country['cities'] as $city){
      echo 'City ID: '.$city['city_id'].'<br/>';
      echo 'City Name: '.$city['city_name'].'<br/>';
   }

}

Answer 3

Taking the output of one query and mailmerging it into another query in a nested loop is an anti-pattern. Use a join:

select country_ID, country_name,
  City_Id, city_name
From countries cn
Inner join cities ct
On CT.country_id = cn.country_ID

Then....

$cities=array();
$country_names=array();

While($r=mysqli_fetch_array($handle)) {
     $country_names[$r['country_id']]=$r['country_name'];
     If (!is_array($cities[$r['country_id'])) $cities[$r['country_id']]=array();
     $cities[$r['country_id']][$r['city_id']]=$r['city_name'];
}