如果你数据表里保存的是xml数据：
such as:
<order version="1.0" orderid="123669425" orderid_parent="" shopid="" unionName="doumai" userid="102138995730010" is_newbuyer="" input_type="get" buydate="2013-09-25 19:06:54" paydate="" total_price="23.40" total_commission="" username="" tracking_code="" fld="" fanli="" point="" consume_status="" consume_time="" platform="" consumed="" pay_status="" pay_type="" order_status="" deli_name="" deli_no="" complete="0" status_sign=""><products><product product_id="0" total_price="23.40" total_num="1" commission_id="" commission="0" fanli="" point="" product_title="" category_id="" category_title="" product_url="" consume_status="" status_sign=""/></products></order>
那么使用php调用mysql时报错：
Unicode data in a Unicode-only collation or ntext data cannot be sent to clients using DB-Library (such as ISQL) or ODBC version 3.7 or earlier.
原因可以看这里：
http://hi.baidu.com/tylzyoudi/item/bd087657d519979408be177c
大概意思是,这是因为我们的pymssql使用早期的ODBC函数集来获取数据。后来微软才引入了ntext和nvarchar类型，但Microsoft并没有更新他们的 C-library，所以就没办法支持了。建议：将ntext修改为nvarchar或text.
显然，这不是个好的解决方法，那么是否就没有其他办法了呢?
还好，不用绝望，既然不支持ntext但支持text，那么我们只需要在输出时将ntext转换为text就好了，方法很简单：
SELECT cast ( field_name AS TEXT ) AS field_name之后我们就cast(orderxml as TEXT)，发现依旧报错:
Explicit conversion from data type xml to text is not allowed.
然后我们看这里：
http://www.php.net/manual/zh/ref.mssql.php
发现是要这样：
4. So you cannot read the VARCHAR nor the XML, and you cannot transform the XML into TEXT. In order to finally read that XML field-type, you may use this trick :
"SELECT CAST(CAST([xmlfield] AS VARCHAR(8000)) AS TEXT) FROM [table]"
所以我们这样：
select cast(cast(orderxml as varchar(8000)) as TEXT) as orderxml
终于可以解决问题了~~