MYSQL检查数据库中是否已存在用户名[重复]

Question

This question already has an answer here:

• Can I mix MySQL APIs in PHP? 4 answers

My code was working but after I inserted a query to check if the first name in MYSQL database already exists, it does not work anymore. Here you can see my code, if you have any tip on how to make this work, I will appreciate it. Thank you very much!

I have tried to work with mysql_num_rows command, but it seems like I didn't use it correctly.

<?php 

require_once __DIR__.'/connect.php';

$sName = $_POST['txtName'];

$query = mysql_query("SELECT * FROM users WHERE firstName = '$sName' ");
if (mysql_num_rows ($query) > 0){
    echo 'User with this name already exists';
}else{
    try {
        $stmt = $db->prepare('INSERT INTO users
    VALUES (null, :sName, :sLastName, :sEmail, :sCountry )');
        $stmt->bindValue(':sName', $sName);

        $stmt->execute();
        echo 'New user was successfully inserted';
    } catch (PDOEXception $ex) {
        echo $ex;
    }
}

</div>

Answer 1

You are trying to use mysql_query when you have (based on the rest of your code that is working) a PDO connection. Change your query to use your existing connection:

try {
    $stmt = $db->prepare("SELECT COUNT(*) FROM users WHERE firstName = :sName");
    $stmt->bindValue(':sName', $sName);
    $stmt->execute();
    $num_rows = $stmt->fetchColumn();
}
catch (PDOEXception $ex) {
    echo $ex;
}
if ($num_rows > 0) {
    echo 'User with this name already exists';
}
else {
    // the rest of your code here