生成唯一标识uuid

方法一

function greate_uuid()
{
    if (version_compare(PHP_VERSION, '7.1', '>=')) {
        return md5(session_create_id());
    }
    return md5(uniqid(md5(microtime(true)), true));
}

方法二
/**

• 生成UUID 单机使用
• @access public
• @return string
  */
  function uuid()
  {
  $charid = md5(uniqid(mt_rand(), true));
  $hyphen = chr(45); // “-“
  $uuid = chr(123) // “{“
  . substr($charid, 0, 8) . $hyphen
  . substr($charid, 8, 4) . $hyphen
  . substr($charid, 12, 4) . $hyphen
  . substr($charid, 16, 4) . $hyphen
  . substr($charid, 20, 12)
  . chr(125); // “}”
  return $uuid;
  }

测试方法
//生成指定数量的uuid
$uuids = [];
for ($i = 0; $i < 1000000; $i++) {
$uuids[] = greate_uuid();
}
//统计数据中值出现的次数
$values = array_count_values($uuids);
//遍历出大于1次的uuid
$duplicates = [];
foreach ($values as $k => $v) {
if ($v > 1) {
$duplicates[$k] = $v;
}
}
echo ‘<pre>';
print_r($duplicates);
echo '</pre>‘;