如何在mysqli-prepared-starement中使用多个内部联接以及多个WHERE子句？[副本]

Question

我正在尝试编写一个查询，其中我希望根据第一个连接条件选择WITHWHERE子句，并根据第二个连接条件选择第二个where子句。我用了几种方法编写了它，但它总是显示出一个错误：

Fatal error: Call to a member function bind_param() on boolean in /var/www/html/connections.php on line 80

$user_id正在从其他地方获取。所以没有问题，如果我在这里运行一个连接，它工作正常。

我的问题是：

方法1：

$sql = $db->prepare("SELECT r.* from registered_users r 
        inner join connections c2 on r.id = c2.uid
        inner join connections c on r.id = c.connections_userid where c2.connections_userid = ? or c.uid = ?");

$sql->bind_param("ii",$user_id,$user_id);           
$sql->execute();

方法二：

$sql = $db->prepare("SELECT r.* from registered_users r 
        inner join connections c2 on r.id = c2.uid where     c2.connections_userid = ?
        inner join connections c on r.id = c.connections_userid where c.uid = ?");

$sql->bind_param("ii",$user_id,$user_id);           
$sql->execute();

Answer 1

您的准备有错误，请检查它

$sql = $db->prepare("SELECT r.* from registered_users r 
    inner join connections c2 on r.id = c2.uid
    inner join connections c on r.id = c.connections_userid where c2.connections_userid = ? or c.uid = ?");

if (!$sql) {
   //error !! Let's report it!
   trigger_error($db->error);
}

$sql->bind_param("ii",$user_id,$user_id);           
$sql->execute();