MySQLi第二个查询不起作用

Question

我试图在一个php页面内使用查询两次时遇到MySQLi和PHP的问题。问题是，第一个查询完美，但第二个不起作用。第一个查询设置了会话，但第二个查询不。这里是我的代码（我也有连接到数据库文件，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

更换else if

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

随着if

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

的问题你的代码是只要第一个查询成功运行，执行永远不会进入else if（即使第一个查询没有返回结果，它仍然运行succ essfully）。为了经常检查这两个条件，则需要分开单独if块

这两个

PS：这将是更有效地运行一个查询，你应该永远插入用户提供的值，如$username直接在您的疑问;这是为了避免SQL注入。你的代码非常脆弱。这里是一个更安全，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 
}