检查数据库用户名是否已存在 PHP v5

无法弄清楚这一点，不知道是不是因为我使用的是 v5+，但">mysqli_num_rows($result(> 0"没有按预期工作......但它仍在将变量注入数据库。

我收到的错误是">警告：mysqli_num_rows(( 期望参数 1 mysqli_result，布尔值在第 22 行的 C：''xampp''htdocs''lichie''register.php 中给出'">

我在堆栈溢出上看到的其他示例可以使用">mysql_query"方法，但我正在尝试使用">mysqli_query"。

这是代码：

<?php
include "connect_db_users.php";
@$username = strtolower($_POST['user']);
@$email = strtolower($_POST['email']);
@$pass = $_POST['pass'];
@$confirmPass = $_POST['confirmPass'];
$ins_user = "INSERT INTO lichie_user(user_user,user_pass,user_email, user_date)"
            . "VALUES ('" . $username . "' , '" . $pass . "' , '" . $email . "' , NOW())";
if(isset($_POST['submit'])){
    if($username == !''){
        if($email == !''){
            if($pass == !''){
                if($pass == $confirmPass){
                    $query = 'SELECT user_user FROM lichie_user WHERE user_user=$username';
                    $result = mysqli_query($connect,$query);
                    if (mysqli_num_rows($result) > 0){
                        echo "Username already exists!";
                    }else{
                        if(mysqli_query($connect, $ins_user)){
                            mysqli_close($connect);
                            /*header("Location: Success.php");*/
                            echo "INSERTED";
                        }else{
                            echo "FAILED!";
                        }
                    }
                }else{
                    echo "Passwords do not match!";
                }
            }else{
                echo "Password can not be empty!";
            }
        }else{
            echo "Email can not be empty!";
        }
    }else{
        echo "Username can not be empty!";
    }
}


?>


<form method="POST">
    <h2 align="center"> Register</h2>
    <table id="table1"; cellspacing="5px" cellpadding="5%"; align="center">
            <tr>
                <td align="right">Username:</td>
                <td><input type="text" name="user" /></td>
            </tr>
            <tr>
                <td valign="top" align="right">Email:</td>
                <td><input type="email" name="email" /></td>
            </tr>
            <tr>
                <td valign="top" align="right">Password:</td>
                <td><input type="password" name="pass" autocomplete="off" /></td>
            </tr>
            <tr>
                <td valign="top" align="right">Confirm Password:</td>
                <td><input type="password" name="confirmPass" autocomplete="off"/></td>
            </tr>
            <tr>
                <td><input type="submit" name="submit" value="submit"/></td> 
            </tr>
    </table> 
</form>