使用php从mysql数据库检索信息时出错

Question

我无法从mysql数据库中检索信息。我收到了一个错误

  

数组\ n（\ n [0] =＆gt; 42000 \ n [1] =＆gt; 1064 \ n [2] =＆gt;在客户端

然而，当我用常规字符串替换变量 $ city 时，像＃34;旧金山＆＃34;它工作正常。我甚至测试过 $ city 是否是一个字符串，它是一个字符串

$ sth 即使查询成功也无法执行

 <?php

    if (isset($_GET)) {

        $servername = "localhost";
        $username = "XXXXX";
        $password = "XXXXX";
        $dbname = "CALIFORNIA";
        $city = $_GET['userinput'] . "";


        // Create connection
        $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
        $conn->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, PDO::ATTR_ERRMODE, PDO::ERRMODE_WARNING);
        $sql = "SELECT State FROM  CITY WHERE City_name = $city";   // When I replace the $city with string like "San Francisco", it works but not with variable $city

        if (($sth = $conn->prepare($sql))) {
            if ($sth->execute()) {            // $sth failed even though the query was successful 
                $result = $sth->fetchAll();
                $json = json_encode($result);
                echo $json;
            }
            else
                echo print_r($sth->errorInfo()); // Error print out on client side

        }
        else
            echo  $conn->errorCode();

        }