PHP PDO左连接多维数组

Question

Basically, I have three tables. I have a projects table, a questions table and an answers table. A project can have many questions and a question can have many answers. Using PDO's and LEFT JOIN ON the Question ID, how can I turn comments with answers into a multidimensional array so that the structure would look like this:

[Question] => Array
    (
        [id] => 1
        [question] => 'Random Question'
        [askedBy] => 123
        [answer] => Array
            (
              [0] => Array
                 (
                   [id] => 1
                   [answer] => 'An Answer'
                   [answeredBy] => 123
                 )
               [1] => Array
                 (
                   [id] => 1
                   [answer] => 'Another Answer'
                   [answeredBy] => 123
                 )
            )
      )

Finalized Code (which is returning what I want)

$questions = array();
$questionCounter = 0;
$questionID = NULL;


$STH = $DBH->query("SELECT `project_question`.`id` AS question_id, `project_question`.`question`, `project_question`.`userID` AS askedBy, 
                               `project_question`.`created` AS question_created, `project_answer`.`id` AS answer_id, 
                               `project_answer`.`answer`, `project_answer`.`userID` AS answeredBy, 
                               `project_answer`.`accepted`, `project_answer`.`created` AS answer_created
                          FROM `project_question`
                     LEFT JOIN `project_answer`
                            ON `project_question`.`id` = `project_answer`.`questionID`
                         WHERE `project_question`.`projectID` = $args[0]
                           AND `project_question`.`projectPhase` = 2");

    while($row = $STH->fetch(PDO::FETCH_ASSOC)){
      if($row['question_id'] !== $questionID){
        $questions[$questionCounter] = array(
            'id' => $row['question_id'],
            'question' => $row['question'],
            'userID' => $row['askedBy'],
            'created' => $row['question_created'],
            'answers' => array()                  
        );
        array_push($questions[$questionCounter]['answers'], 
             array(
              'id' => $row['answer_id'],
              'answer' => $row['answer'],
              'userID' => $row['answeredBy'],
              'accepted' => $row['accepted'],
              'created' => $row['answer_created']
        ));
        $questionCounter++;
        $questionID = $row['question_id'];
      } else {
        array_push($questions[$questionCounter - 1]['answers'], 
             array(
              'id' => $row['answer_id'],
              'answer' => $row['answer'],
              'userID' => $row['answeredBy'],
              'accepted' => $row['accepted'],
              'created' => $row['answer_created']
        ));
      }          
    }

Answer 1

In one query, you can request all answers, join questions to them, and join projects to questions.

1. Create empty array $projects = array()
2. Iterate through every resulting row foreach ($rows as $row)
3. Add project with its data to array, if it does not exist already (use project id as key) if (!isset($projects[$row->project_id])) { $projects[$row->project_id] = array('col1' => $row->col1,'questions' => array()); } if (!isset($projects[$row->project_id])) { $projects[$row->project_id] = array('col1' => $row->col1,'questions' => array()); }
4. Add question with its data to project questions array, if it does not exist already (use question id as key) if (!isset($projects[$row->project_id]['questions'][$row->question_id])) { $projects[$row->project_id]['questions'][$row->question_id] = array('col2' => $row->col2,'answers' => array()); } if (!isset($projects[$row->project_id]['questions'][$row->question_id])) { $projects[$row->project_id]['questions'][$row->question_id] = array('col2' => $row->col2,'answers' => array()); }
5. Add answer with its data to project question answers array (use answer id as key) $projects[$row->project_id]['questions'][$row->question_id]['answers'][$row->answer_id] = array('col3' => $row->col3);

But as you can understand, you will get many useless information in that query. You could go with one query, getting projects only, iterate through them, in each cycle add data to array and query again to get questions that has specific project_id, iterate through them, in each cycle add data to array and query again to get answers that has specific question_id, iterate through them, and add data to array.

But if I rethink this, I think MySQL will work faster than PHP, even with returning bunch of useless data (I mean, repeating data about projects and questions) and 1 query vs possible 50 queries from one client is much better, so I suggest better use first method.

Without further information about your database table and columns, you wont get from me anything more than pseudo-code-algorithm.

EDIT: Possible MySQL select query:

SELECT 
    a.id answer_id, a.answer, a.answeredBy, 
    q.id question_id, q.question, q.askedBy, 
    p.id project_id, p.title
FROM answer a
LEFT JOIN question q ON q.id = a.question_id
LEFT JOIN project p ON p.id = q.project_id

For table structure

• project -> | id | title |
• question -> | id | question | askedBy | project_id |
• answer -> | id | answer | answeredBy | question_id |