1

我想从表中选择随机行并从此处的其他问题中获得以下代码，但我有点困惑将表名和列名放在哪里，因为我以前从未使用 mysqli 进行过此类选择。有人可以帮帮我吗？我的表名是products，列名是title。

我正进入（状态：

Fatal error: Call to a member function execute() on a non-object

这是代码：

  SELECT name
  FROM random AS r1 JOIN
   (SELECT (RAND() *
                 (SELECT MAX(id)
                    FROM random)) AS id)
    AS r2
 WHERE r1.id >= r2.id
 ORDER BY r1.id ASC
 LIMIT 1

我尝试了什么：

 $mydb = new mysqli('localhost', 'root', '', 'db');
    $stmt = $mydb->prepare("SELECT title
            FROM products AS r1 JOIN
               (SELECT (RAND() *
                 (SELECT MAX(id)
             FROM random)) AS id)
            AS r2
     WHERE r1.id >= r2.id
     ORDER BY r1.id ASC
     LIMIT 1 ");
 $stmt->execute();
4

2 回答 2

0

看看prepare后有没有报错：

 $mydb = new mysqli('localhost', 'root', '', 'db');
    $stmt = $mydb->prepare("SELECT title
            FROM products AS r1 JOIN
               (SELECT (RAND() *
                 (SELECT MAX(id)
             FROM random)) AS id)
            AS r2
     WHERE r1.id >= r2.id
     ORDER BY r1.id ASC
     LIMIT 1 ");
if ( false===$stmt ) {
  die('prepare() failed: ' . htmlspecialchars($mydb ->error));
}
于 2013-08-21T23:44:30.717 回答
0

我最近为我所有的 sql 函数制作了一个 sql 驱动程序，获得随机记录就是其中之一。

阅读评论后，我从这个博客改编了解决方案＃3，这就是我想出的：



<?php 

class MyDatabaseDriver {
    protected $DBC;
    protected $SEL_RANDOM_OFFSET;
    protected $SEL_RANDOM_IMAGE;

function __construct($uname, $password, $table="my_table") {
    $this->DBC = new mysqli('localhost', $uname, $password, $table);

    if ($this->DBC->connect_errno) {
        printf("Connect failed: %s\n", $this->DBC->connect_error);
        exit;
    }

    $this->initialize();
}

function __destruct() { $this->close(); }


protected function initialize() {
    $this->SEL_RANDOM_OFFSET = $this->DBC->prepare("SELECT ROUND(RAND() * COUNT(*), 0) AS `offset` FROM `images` WHERE `albumid` = ?");
    $this->SEL_RANDOM_IMAGE = $this->DBC->prepare("SELECT `filename` FROM `images` LIMIT ?, 1");
}

function close() {
    if (!$this->DBC) return;
    $this->SEL_RANDOM_OFFSET->close();
    $this->SEL_RANDOM_IMAGE->close();
    $this->DBC->close();
    $this->DBC = false;
}

function SelectRandomImage($gid) {
    $result = false;
    $this->SEL_RANDOM_OFFSET->bind_param("i", $gid);
    $this->SEL_RANDOM_OFFSET->execute();
    $this->SEL_RANDOM_OFFSET->bind_result($result);

    if (!$this->SEL_RANDOM_OFFSET->fetch()) {
        printf("Select random offset failed: %s\n", $this->SEL_RANDOM_OFFSET->error);
        $result = false;
        $this->SEL_RANDOM_OFFSET->reset();
        return $result;
    }

    $this->SEL_RANDOM_OFFSET->reset();
    $this->SEL_RANDOM_IMAGE->bind_param("i", $result);
    $this->SEL_RANDOM_IMAGE->execute();
    $this->SEL_RANDOM_IMAGE->bind_result($result);

    if (!$this->SEL_RANDOM_IMAGE->fetch()) {
        printf("Select random image failed: %s\n", $this->SEL_RANDOM_IMAGE->error);
        $result = false;
        $this->SEL_RANDOM_IMAGE->reset();
        return $result;
    }

    $this->SEL_RANDOM_IMAGE->reset();
    return $result;
}

} ?>

afaik，这是目前在不同虚拟主机之间具有最佳兼容性的解决方案（从本地迁移到远程主机时，我在使用“get_result”等时遇到了一些问题）。它还考虑到准备好的语句可以以更高的效率重复多次（这是关于 #3 的抱怨之一是它必须重复才能获得多个结果），因此对象被重置并保持活动状态，直到类超出范围或直接调用close。

编辑：在我的偏移选择中，我使用“ROUND”，因为我的数据库 ID 列以 1 开头，如果您的 ID 列以 0 开头，您可能想要使用“FLOOR”

于 2013-10-11T16:54:29.050 回答