PHP选择MySQL提供未知错误

我遇到了一个php脚本的问题，我正在尝试。因此，当我启动它时，脚本完美地连接到MySQL和数据库，但当我尝试从“codes”数据库中选择数据时，它会给我一个类似这样的错误：“无法获取数据：”。它应该做的是说“无法获取数据：（然后这里出现错误）”，但它没有。提前感谢。：）

PHP代码：

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

// Create connection
$conn = mysqli_connect($servername, $username, $password);
mysqli_select_db($dbname);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";

   $sql = 'SELECT code FROM codes';
   $retval = mysql_query( $sql, $conn );

   if(! $retval ) {
      die('Could not get data: ' . mysql_error());
   }

   while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) {
      echo "Code:{$row['code']}";
   }

   echo "Fetched data successfully\n";

   mysql_close($conn);  
?>

---

您将mysql和mysqli混合在一起，因此我修复了错误：

<?php
ini_set('display_errors', 1); 
error_reporting(E_ALL);
$servername = "localhost";
$username = "root";
$password = "pass";
$dbname = "table";

// Create connection
$conn = mysqli_connect($servername, $username, $password);
        mysqli_select_db($conn, $dbname);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
// echo "Connected successfully";

   $sql = 'SELECT username FROM users';
   $retval = mysqli_query($conn ,$sql);

   if(! $retval ) {
      die('Could not get data: ' . mysqli_error());
   }

   while($row=mysqli_fetch_array($retval,MYSQLI_ASSOC)) {
      echo "Code:{$row['username']}";
   }

   echo "Fetched data successfully\n";

   mysqli_close($conn);  
?>

您将mysql和mysqli混合在一起，因此我修复了错误：

<?php
ini_set('display_errors', 1); 
error_reporting(E_ALL);
$servername = "localhost";
$username = "root";
$password = "pass";
$dbname = "table";

// Create connection
$conn = mysqli_connect($servername, $username, $password);
        mysqli_select_db($conn, $dbname);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
// echo "Connected successfully";

   $sql = 'SELECT username FROM users';
   $retval = mysqli_query($conn ,$sql);

   if(! $retval ) {
      die('Could not get data: ' . mysqli_error());
   }

   while($row=mysqli_fetch_array($retval,MYSQLI_ASSOC)) {
      echo "Code:{$row['username']}";
   }

   echo "Fetched data successfully\n";

   mysqli_close($conn);  
?>

您正在组合
mysql
&
mysqli
。仅在每次操作中使用mysqli
如果您将mysqli与mysqli混合使用，请检查您的数据库名称。如果您完全使用Mysql或MysqliThanks，则我已将所有Mysql都切换到mysqli。但是它仍然给了我一个没有解释的错误，你正在结合
mysql
&
mysqli
。仅在每次操作中使用mysqli
如果您将mysqli与mysqli混合使用，请检查您的数据库名称。如果您完全使用Mysql或MysqliThanks，则我已将所有Mysql都切换到mysqli。但它仍然给我一个错误，没有解释