检查记录是否存在数据库 - 错误显示

如何检查用户名或电子邮件是否存在，然后将错误消息放入错误数组中。现在我有：

$sql = "SELECT username, email FROM users WHERE username = '" . $username . "' OR email = '" . $email . "'";

$query = mysql_query($sql);

if (mysql_num_rows($query) > 0)
{
 echo "That username or email already exists";
}

但我想检查它是否是用户名或现有的电子邮件，然后输入：

error[] = "用户名已存在"; //如果用户名存在

error[] = "电子邮件已存在"; //如果电子邮件存在

怎么做？

如果您只是在 SQL 中快速进行真/假检查并检查返回的标志，那就会更容易。

$sql = "SELECT "
  . "(SELECT 1 FROM `users` WHERE `username` = '" . mysql_real_escape_string($username) . "'), "
  . "(SELECT 1 FROM `users` WHERE `email` = '" . mysql_real_escape_string($email) . "')";

$query = mysql_query($sql);

if (mysql_num_rows($query) > 0) {
  $foundFlags = mysql_fetch_assoc($query);
  if ($foundFlags['username']) {
    $error[] = "username is existing";
  }

  if ($foundFlags['email']) {
    $error[] = "email is existing";
  }
} else {
  // General error as the query should always return
}

当它没有找到条目时，它将在标志中返回 NULL，其计算结果为 false，因此if条件很好。

请注意，您可以将其概括为字段列表，如下所示：

$fieldMatch = array('username' => $username, 'email' => $email);

$sqlParts = array();
foreach ($fieldMatch as $cFieldName => $cFieldValue) {
  $sqlParts[] = "(SELECT 1 FROM `users` WHERE `" . $cFieldName . "` = '" . mysql_real_escape_string($cFieldValue) . "')";
}


$sql = "SELECT " . implode(", ", $sqlParts);

$query = mysql_query($sql);

if (mysql_num_rows($query) > 0) {
  $foundFlags = mysql_fetch_assoc($query);
  foreach ($foundFlags as $cFieldName => $cFlag) {
    if ($foundFlags[$cFieldName]) {
      $error[] = $cFieldName . " is existing";
    }
  }
} else {
  // General error as the query should always return
}

NB.请注意，假设所有字段都是字符串或其他字符串转义类型（例如日期/时间）。