MySQL UPDATE语句在查询中有效，但在PHP代码中无效

When I execute the statement in phpmyadmin, it works properly, but when I copy and paste the exact same query into this php file, it doesn't work.

PHP Code:

if($_GET['vote'] == 1) {
    echo "if statement ran";
    $sql = "UPDATE raids SET attendees = attendees +1 WHERE dateposted =  '2017-08-19 16:15:46'";
    mysql_query($sql, $link);
}

My link variable does work and the 'if' statement executes. Other SQL statements haven't given me trouble.

Why isn't the php code incrementing 'attendees' when used in the PHP code?

As Milan Chheda said, MySQL is deprecated and is no longer secure. Use PDO or at least MySQLi instead.

MySQLi implementation for your code:

    //MySQLi information

    $db_host     = "localhost";
    $db_username = "username";
    $db_password = "password";

    //connect to mysqli database (Host/Username/Password)
    $connection = mysqli_connect($db_host, $db_username, $db_password) or die("Error " . mysqli_error());

    //select MySQLi dabatase table
    $db = mysqli_select_db($connection, "table") or die("Error " . mysqli_error());

    if(isset($_GET['vote']) && $_GET['vote'] !== NULL) {

$vote = $_GET['vote'];

if($vote == "1") {
    echo "Vote is 1, updating the database";
    $sql = mysqli_query($connection, "UPDATE raids SET attendees = attendees + '1' WHERE dateposted =  '2017-08-19 16:15:46'");
}

}

I hope this helped you. Good luck!