如何在mysqli準備的stanment中使用多個內部連接以及多個WHERE子句？

Question

我想寫一個查詢，我想根據第一個連接條件選擇WHERE子句，第二個連接是基於第二個WHERE子句。我已經寫了幾種方法，但它總是顯示一個錯誤：

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

$ user_id正在從其他地方獲取。所以沒有問題，如果我在這裏運行單個連接，它工作正常。

這裏是我的查詢：

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2：

$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

你必須與你準備一個錯誤，因此，應檢查

$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();