SQL查询在PHP中返回null，但在MySQL中是正确的结果

问题描述：

I'm building a web application for inserting data into a MySQL database. I'm using PHP's PDO API to query the database to obtain an auto-incrementing primary key. When I run the query in MySQL Console, it produces the correct output. But when I try to run the query in PHP, it returns null.

Query:

mysql> SELECT Auto_Increment FROM information_schema.tables WHERE table_name='charlist';

Result in MySQL console:

+----------------+
| Auto_Increment |
+----------------+
|              7 |
+----------------+

Relevant PHP code:

    // Configuration.
    $username = "root";
    $password = "root";
    $hostname = "localhost";
    $dbname = "asoiaf";
    $tablename = "charlist";

    // Opens a connection to the database.
    try {
        $conn = new PDO("mysql:host=$hostname;dbname=$dbname", $username, $password);
        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    } catch(PDOException $e) {
        echo $e->getmessage();
    }

    // Gets all the information from POST.
    $autoidquery = "SELECT Auto_Increment FROM information_schema.tables WHERE table_name='$tablename'";
    $id = $conn->query("SELECT Auto_Increment FROM information_schema.tables WHERE table_name='$tablename'");
    // This should output the auto-incremented primary key, but nothing is output.
    echo $id."<br>Hello world";

Nothing is output on the page, although it should output the auto-incremented id and then "Hello world". I can't see any typos that I've made. Why would the query work in the console, but not in PHP?

我正在构建一个用于将数据插入MySQL数据库的Web应用程序。我正在使用PHP的PDO API来查询数据库以获取自动递增的主键。当我在MySQL控制台中运行查询时，它会生成正确的输出。但是当我尝试在PHP中运行查询时，它返回null。 p>

查询： p>

  mysql＆gt;  SELECT Auto_Increment FROM information_schema.tables WHERE table_name ='charlist'; 
  code>  pre> 
 
  MySQL控制台中的结果： p> 
 
 
  +  ---------------- + \ N |  Auto_Increment | 
 + ---------------- + 
 |  7 | 
 + ---------------- + 
  code>  pre> 
 
 相关的PHP代码： p> 
 
  
  // Configuration。
 $ username =“root”; 
 $ password =“root”; 
 $ hostname =“localhost”; 
 $ dbname =“asoiaf”; 
 $ tablename  =“charlist”; 
 
 //打开与数据库的连接。
尝试{
 $ conn = new PDO（“mysql：host = $ hostname; dbname = $ dbname”，$ username，$ password）  ; 
 $ conn-＆gt; setAttribute（PDO :: ATTR_ERRMODE，PDO :: ERRMODE_EXCEPTION）; 
} catch（PDOException $ e）{
 echo $ e-＆gt; getmessage（）; 
} 
 
  //从POST获取所有信息。
 $ autoidquery =“SELECT Auto_Increment FROM information_schema.tables WHERE table_name ='$ tablename'”; 
 $ id = $ conn-＆gt; query（“SELECT Auto_Increment FROM information_schema.tables WHERE  table_name ='$ tablename'“）; 
 //这应输出自动递增的主键，但不输出任何内容。
 echo $ id。”＆lt; br＆gt; Hello world“; 
  code>  
 
 页面上没有输出任何内容，但应输出 自动递增的id然后是“Hello world”。 我看不到任何打字错误。 为什么查询在控制台中工作，而在PHP中不起作用？ p> 
  div>

答

You need to fetch the result

$qry = $conn->query("SELECT Auto_Increment FROM information_schema.tables WHERE  table_name='$tablename'");
$result = $qry->fetch();
$id = $result['Auto_Increment'];
echo $id."<br>Hello world";

答

PDO Query returns a PDO Statement, to access the desired result you need to access the result as an array.

echo $id['Auto_Increment'];

Or you could fetch the result from the statement

echo $id->fetchColumn();

Or use PDO Prepare + fetchColumn to retrieve the result as an integer.

Many ways lead to rome ;)

答

use : print_r($id);

to see the content of query result . the output of the query result is an array. you shou

SQL查询在PHP中返回null，但在MySQL中是正确的结果

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