file field not properly work for file upload

I am creating pdf file uploader. And I have created custom field (type=file type). but this field not save after brows the file. So guide me how i can success to doing so.When I click on save button then i am facing following error.
"Error
Save failed with the following error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'select FROM #__pdfperfectuploader_ WHERE id = 0' at line 1 SQL=SELECT select FROM #__pdfperfectuploader_ WHERE id = 0"