使用PHP检查MySQL表中是否存在用户名？ [重复]

Question

This question already has an answer here:

• mysql_fetch_array()/mysql_fetch_assoc()/mysql_fetch_row()/mysql_num_rows etc… expects parameter 1 to be resource or result 32 answers

I want to create a code to check if username already exists on server or not using MySQL and PHP. The code:

// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());
}
$sql = "SELECT username FROM Servers where email=".$user_info['email']."";
$result = mysqli_query($conn, $sql);
if (mysqli_num_rows($result) > 0) {
//username exists
}
else
{
 //...
}

I keep getting this error:

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in

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Answer 1

Use this-

$sql = "SELECT username FROM Servers where email='".$user_info['email']."'";