extract data into json

I retrieved MySQL data from three tables in XML using PHP:

$table_first = 'recipe';
$query = "SELECT * FROM $table_first";
$resouter = mysql_query($query, $conn);

$doc = new DomDocument('1.0');

$root = $doc->createElement('recipes');
$root = $doc->appendChild($root);

while($row = mysql_fetch_assoc($resouter)){

$outer = $doc->createElement($table_first);
$outer = $root->appendChild($outer);

 foreach ($row as $fieldname => $fieldvalue) {
    $child = $doc->createElement($fieldname);
    $child = $outer->appendChild($child);
    $value = $doc->createTextNode($fieldvalue);
    $value = $child->appendChild($value);
  }// foreach
 //while

  $table_second='instructions';
$query="SELECT instructions.instruction_id,instructions.instruction_text FROM $table_second where rec_id = ".$row['rec_id'];
$resinner=mysql_query($query, $conn);

$inner = $doc-&g开发者_如何学Pythont;createElement($table_second);
    $inner = $outer->appendChild($inner);
 while($row1 = mysql_fetch_assoc($resinner)){

    $inner1=$doc->createElement('instruction');
    $inner1=$inner->appendChild($inner1);

    foreach ($row1 as $fieldname => $fieldvalue) {
        $child = $doc->createElement($fieldname);
        $child = $inner1->appendChild($child);
        $value = $doc->createTextNode($fieldvalue);
        $value = $child->appendChild($value);
    } // foreach
 }// while

$table_third='ingredients';

$query="SELECT ingredients.ingredient_id,ingredients.ingredient_name,ingredients.ammount FROM $table_third where rec_id = ".$row['rec_id'];
$resthird=mysql_query($query, $conn);


 $inner=$doc->createElement($table_third);
    $inner=$outer->appendChild($inner);

while($row=mysql_fetch_assoc($resthird)){
$inner2=$doc->createElement('ingredient');
    $inner2=$inner->appendChild($inner2);
foreach($row as $fieldname=> $fieldvalue)
    {
        $child=$doc->createElement($fieldname);
        $child=$inner2->appendChild($child);
        $value=$doc->createTextNode($fieldvalue);
        $value=$child->appendChild($value);
}
}
}

mysql_close($conn);
$xml_string = $doc->saveXML();
echo $xml_string;
?>

This works perfectly, but now I want to retrieve that data in JSON. I retrieved data from one table using JSON, but how to retrieve the same data from these three tables using JSON instead of XML?

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Create arrays in PHP and use json_encode() on your structure.