Combine 2 arrays by matching the same foreign key

Question

I have 2 table, that is a question_table and answer_table the structure is like this :

And I have a JSON array that I got from question_table and answer_table using php

Answer 1

Can you try following code:

$sql = "select q.id, q.question, a.aswer from question_table q inner join answer_table a ON q.id = a.id_question”;
$resultPertanyaan = mysqli_query($con, $sql);

while($rowQuery= mysqli_fetch_array($resultPertanyaan)){
   $array_result[]= 
array('id'=>$rowQuery['id’],’question’=>$rowQuery['question'], 'answer' => $rowQuery['aswer']);
}

Answer 2

You can use array_map to process each of the questions, looking for an answer in $array_answer for each one:

$questions = json_decode($array_question);
$answers = json_decode($array_answer, true);

$array_result = array_map(function ($v) use ($answers) {
    $v->answer = ($k = array_search($v->id, array_column($answers, 'id_question'))) !== false ? $answers[$k]['answer'] : null;
    return $v;
}, $questions);
print_r(json_encode($array_result, JSON_UNESCAPED_SLASHES));

Output:

[{"id":"8","question":"Shop sign/billboard ","answer":null},
 {"id":"10","question":"Pylon","answer":null},
 {"id":"11","question":"Banner","answer":"1"},
 {"id":"12","question":"Sport","answer":"3"},
 {"id":"14","question":"Matic ","answer":"1"},
 {"id":"16","question":"Cub","answer":"3"}
]

Demo on 3v4l.org

Update

For versions of PHP prior to 5.4, there are a couple of issues with the above code. Firstly array_column was not implemented in PHP until version 5.5.0. Secondly the JSON_UNESCAPED_SLASHES constant and associated functionality wasn't implemented until PHP 5.4.0. We can emulate those with this code:

function my_array_column($array, $column) {
    return array_map(function ($v) use ($column) { return $v[$column]; }, $array);
}

$array_result = array_map(function ($v) use ($answers) {
    $v->answer = ($k = array_search($v->id, my_array_column($answers, 'id_question'))) !== false ? $answers[$k]['answer'] : null;
    return $v;
}, $questions);
echo str_replace('\/', '/', json_encode($array_result));

Demo on 3v4l.org