MySQLi第二個查詢不起作用

Question

我試圖在一個php頁面內使用查詢兩次時遇到MySQLi和PHP的問題。問題是，第一個查詢完美，但第二個不起作用。第一個查詢設置了會話，但第二個查詢不。這裏是我的代碼（我也有連接到數據庫文件，表格及其它文件）..

$connection = new mysqli($server,$username,$password,$database); 

$username = $_POST['username']; 
$email = $_POST['email']; 

if($select1 = $connection->query("SELECT * FROM users WHERE username = '$username'")) { 
    $counter1 = $select1->num_rows; 
    if($counter1 != 0) { 
     $_SESSION["accesserror"] = "Error: <em>That username is already used by other member.</em>"; 
    } 
} 
else if($select2 = $connection->query("SELECT * FROM users WHERE user_email = '$email'")) { 
    $counter2 = $select2->num_rows; 
    if($counter2 != 0) { 
     $_SESSION["accesserror"] = "Eror: <em>That E-Mail is already used by other member.</em>"; 
    } 
} 

Answer 1

更換else if

else if($select2 = $connection->query("SELECT * ... 

隨着if

if($select2 = $connection->query("SELECT * ... 

的問題你的代碼是隻要第一個查詢成功運行，執行永遠不會進入else if（即使第一個查詢沒有返回結果，它仍然運行succ essfully）。爲了經常檢查這兩個條件，則需要分開單獨if塊

這兩個

PS：這將是更有效地運行一個查詢，你應該永遠插入用戶提供的值，如$username直接在您的疑問;這是爲了避免SQL注入。你的代碼非常脆弱。這裏是一個更安全，更高效的版本：

$username = mysqli_escape_string($_POST['username']); 
$email = mysqli_escape_string($_POST['email']); 
$sql = "SELECT * FROM users WHERE username='$username' OR email='$email'"; 
if($select = $connection->query($sql) && $select->num_rows) { 
    while($row = $select->fetch_assoc()){ 
     if($row['username']===$username){/* add the "username taken" error */} 
     if($row['email']===$email){/*add the "email taken" error */} 
    } 
}elseif($select===false){ 
    //Todo: handle server error. probably a badly formed query 
    //error details in $connection->error 
}else{ 
    // OK to register 
}