使用buttonclick插入sql

Question

您好我想用按钮点击更新我的数据库，并在输入值中写入了什么。

$host = "****";
$conn = db2_connect ($host,"*****", "*********");

    <input id='focusedInput' type='text' name='prodinfo' value=''>  
    <button type='submit' class='btn btn-default' value='Byt information's text'>
    </button>

为什么我对sql的更新不起作用的任何建议？我只能“无法更新数据msg＆＃39;

”

if(isset($_POST['submit']))
{

     if(! $conn ) 
     {
       die('Could not connect: ' . mysql_error());
     }  
    $prodinfo = $_POST['submit'];

    $sql = "UPDATE Persons ". "SET Hobby = $prodinfo". 
           "WHERE Id = 99999" ;

    $retval = mysql_query( $sql, $conn );

    if(! $retval ) {
    die('Could not update data: ' . mysql_error());
     }
    echo "Updated data successfully\n";

    mysql_close($conn);

    }