Question

我正在从数据库中选择一个考试ID列表，然后使用随机的一个从问题列表中进行选择。如果没有匹配的问题，我想选择另一个随机ID，然后重试。这是我现在拥有的代码；它可以运行，但对于某些考试不会返回任何问题。

$query = $connect->prepare("SELECT * FROM exam WHERE level=? AND flag=?");
$query->bind_param("si",$level,$flag);
$query->execute();
$result = $query->get_result();
$resultCount= $result->num_rows;
if($resultCount>0)
{
    while($row=$result->fetch_assoc())
    {   
        $list[]=$row['id'];
   }
    $indexRand=array_rand($list, 1);
    $query->close();
}
$query2 = $connect->prepare("SELECT * FROM questions WHERE exam_id=?");
$query2->bind_param('i', $list[$indexRand]);
$query2->execute();
$question_result = $query2->get_result();
$resultCount2= $question_result->num_rows;
if($resultCount2>0)
{  
    while($questions_rows=$question_result->fetch_assoc())
    {   
        $list2[]=$questions_rows;
    }
}

Answer 1

我会尝试这样的事情（省略代码的第一部分）：

['Will', 'Jon Arryn', 'Jory Cassel', 'Benjen Stark', 'Robert Baratheon', 'Syrio Forel', 'Eddard Stark', 'Viserys Targaryen', 'Drogo', 'Rhaego', 'Mirri Maz Duur', 'Rakharo', 'Yoren', 'Renly Baratheon', 'Rodrik Cassel', 'Irri', 'Maester Luwin', 'Qhorin', 'Pyat Pree', 'Doreah', 'Xaro Xhoan Daxos', 'Hoster Tully', 'Jeor Mormont', 'Craster', 'Kraznys', 'Beric Dondarrion', 'Ros', 'Talisa Stark', 'Robb Stark', 'Catelyn Stark', 'Polliver', 'Tansy', 'Joffrey Baratheon', 'Karl Tanner', 'Locke', 'Rast', 'Lysa Arryn', 'Oberyn Martell', 'The Mountain', 'Grenn', 'Mag the Mighty', 'Pyp', 'Styr', 'Ygritte', 'Jojen Reed', 'Shae', 'Tywin Lannister', 'Mance Rayder', 'Janos Slynt', 'Barristan Selmy', 'Maester Aemon', 'Karsi', 'Shireen Baratheon', 'Hizdahr zo Loraq', 'Selyse Baratheon', 'Stannis Baratheon', 'Myranda', 'Meryn Trant', 'Myrcella Baratheon', 'Jon Snow', 'Areo Hotah', 'Doran Martell', 'Trystane Martell', 'The Flasher', 'Roose Bolton', 'Walda Bolton', 'Unnamed Bolton Child', 'Balon Greyjoy', 'Alliser Thorne', 'Olly', 'Ser Arthur Dayne', 'Osha', 'Khal Moro', 'Three-Eyed Raven', 'Leaf', 'Hodor', 'Aerys II Targaryen, "The Mad King"', 'Brother Ray', 'Lem', 'Brynden Tully (The Blackfish)', 'Lady Crane', 'The Waif', 'Razdal mo Eraz', 'Belicho Paenymion', 'Rickon Stark', 'Jon Umber', 'Wun Weg Wun Dar Wun', 'Ramsay Bolton', 'Grand Maester Pycelle', 'Lancel', 'The High Sparrow', 'Loras Tyrell', 'Mace Tyrell', 'Kevan Lannister', 'Margaery Tyrell', 'Tommen Baratheon', 'Walder Rivers', 'Lothar Frey', 'Walder Frey', 'Lyanna Stark', 'Nymeria Sand', 'Obara Sand', 'Tyene Sand', 'Olenna Tyrell', 'Randyll Tarly', 'Dickon Tarly', 'Thoros of Myr', 'Petyr "Littlefinger" Baelish', 'Ned Umber']

Answer 2

如果我理解正确，则可以在单个数据库查询中完成此操作。

SELECT q.*
  FROM questions q
  LEFT JOIN (
    SELECT e.id
    FROM exams e
    LEFT JOIN questions q ON (e.id = q.exam_id)
    WHERE level = ? AND flag = ? AND q.id IS NOT NULL
    ORDER BY RAND()
    LIMIT 1
  ) i ON (q.exam_id = i.id)
  WHERE i.id = q.exam_id

您以查询表的形式加入子查询。子查询从检查表中选择一个随机项目，然后自身加入问题表，以确保存在一些问题。演示在这里：http://sqlfiddle.com/#!9/b394af/1

如何在PHP

2 个答案: