Question

所以，在mysql中你可以编写这样的嵌入式结构：

$query = mysql_query("SELECT `id` FROM `questions` WHERE `type`='foo';");
while($row = mysql_fetch_array($query, MYSQL_ASSOC)) {
    $query2 = mysql_query("SELECT * FROM `answers` WHERE `question_id`='".$row['id']."'");
    while($row2 = mysql_fetch_array($query2, MYSQL_ASSOC)) {
        echo "Answer id:".$row2['id'];
    }
}

是否可以使用prepare（）在mysqli中执行此操作？如果我写这个：

$mysqli = new mysqli(...);
$stmt = $mysqli->prepare("SELECT `id` FROM `questions` WHERE `type`=?;");
$stmt->bind_param('s','foo');
$stmt->execute();
$stmt->bind_result($question_id);
while ($stmt->fetch()) {
     $stmt2 = $mysqli->prepare("SELECT * FROM `answers` WHERE `question_id`=?");
     die(var_dump($stmt2)); // bool(false)
}

$ stmt2是布尔值false，因为我没有关闭$ stmt。但如果我关闭它，我就无法在循环中访问结果数据。那么，唯一的方法 - 将$ stmt的结果复制到另一个变量，执行$ stmt-＆gt; close（）然后启动while（）循环？或者有其他方法可以做到这一点？

或者我不明白......：）

感谢您的回答！

Answer 1

使用问题主键的联接和排序：

$stmt = $mysql->prepare("SELECT q.*, a.* FROM questions q LEFT JOIN answers a ON (q.id = a.question_id) WHERE q.type = ? ORDER BY q.id");

$stmt->bind_param('s','foo');
$stmt->execute();
$stmt->bind_result($question_id);

$currentQuestion = false;
while ($stmt->fetch()) {
     if($currentQuestion !== $question_id){
       $currentQuestion = $question_id;
       // output question or whatever
     }
     // output answers
}

你必须要小心谨慎的是，如果要返回一个关联数组，那么如果表共享列（例如两个表可能都有id列）那么你只会得到一个价值。要避免这种情况，您需要为列添加别名，这意味着您必须在查询中将它们全部替换为ALL：

SELECT q.id as qid, q.body as qbody, q.type as qtype, a.id as aid, a.body as abody, a.question_id as aqid FROM questions q LEFT JOIN answers a ON (q.id = a.question_id) WHERE q.type = ? ORDER BY qid

mysqli是否支持嵌入式结构？

1 个答案: