使用ORDER BY RAND()和多个WHERE子句mysql

Question

我知道rand()的顺序不是从数据库中绘制随机值的最快方法,但我的数据库很小,而且此时; 我只是想让它起作用!哈哈.这是我的代码:

include('includes/dbc.php');
$top_query = "SELECT * FROM top WHERE 'occasion_id =" . $occasion . "' AND 'temperature_id = " . $temperature . "' AND 'user_id = " . $user_id . "'ORDER BY RAND() LIMIT 1";
$top_result = mysqli_query($dbc, $top_query) or die (' The top SELECT query is broken.');
mysqli_close ($dbc);

while($row= mysqli_fetch_array($top_result)) {
    echo 'This top has an id of:' . $row['top_id']  . '<br> ';
    echo 'Does this top require pants?' . $row['needs_pants']  . '<br>';
    echo 'What\'s the colour id of this top?' . $row['colour_id'] . '<br>';
    echo  $row['value'];
}

出于某种原因,这只是不起作用,当我尝试运行我的数组时,我只会显示空白.它在我通过"rand()limit 1"位投入顺序之前工作,但显然我得到了每个值而不是一个随机值.

谁能看到我哪里出错了？非常感谢!

Answer 1

您的查询格式错误.它并没有消亡,它只是没有返回结果.

请注意错误的单引号:

$top_query = "SELECT * FROM top WHERE 'occasion_id =" . $occasion . "' AND 'temperature_id = " . $temperature . "' AND 'user_id = " . $user_id . "'ORDER BY RAND() LIMIT 1";

您可以通过输出查询然后直接在MySQL中运行它来证明这一点(例如通过PHPMyAdmin):

echo $top_query;

函数mysqli_error()和mysqli_num_rows()帮助确定查询结果.

为了让您继续前进,SQL应该更像:

$top_query = "SELECT * FROM top WHERE occasion_id = '" . $occasion . "' AND temperature_id = '" . $temperature . "' AND user_id = '" . $user_id . "' ORDER BY RAND() LIMIT 1";

一些额外的说明:

• 阅读SQL注入.
• 熟悉MySQL 何时需要引用文字值.在您的情况下,这些都是ID列(理论上是整数),因此不需要引用.
• 注意不要过早关闭MySQL连接.PHP实际上会在脚本结束时自动执行此操作.
• 正如webbiedave评论的那样,也请查看Prepared Statements.