配置错误
PHP Fatal error: Unable to start PDO_DM module in Unknown on line 0
解决办法：配置环境变量path增加C:\dndbms\bin，官方的说明https://eco.dameng.com/document/dm/zh-cn/faq/faq-php.html#PHP%20Fatal%20error:%20Unable%20to%20start%20PDO_DM%20module%20in%20Unknown%20on%20line%200
查询
dm_exec查询的sql语句编码为GB2312，php转换代码：
$sql=mb_convert_encoding($sql,'GB2312');
查询的结果一样是GB2312，需要转换回来：
$data=mb_convert_encoding($result,'UTF-8','GB2312');