Help! pdo:prepared()->execute() didn't return rows.

Dear ALL,

My PHP is running under ubuntu 11.10 in VituralBox. The version returned 
from phpinfo() is:
PHP Version 5.3.6-13ubuntu3.1

PDO supported for mysql. pdo_mysql Client API version is: 5.1.58.

I wrote a stored procedure to insert a row into a table, then select the 
inserted row at the end of the procedure. PDO::query() works fine. I 
change it to PDO:prepared() and PDOStatement->execute() for better 
performance. but the PDOStatement->fetch() return false after true was 
got at PDOStatement->execute().

Could somebody help me, please!!! Thank you.

Best Regards,
Antony