oci_cancel() invalidates a cursor, freeing all associated resources and cancels the ability to read from it.
如果成功则返回 TRUE，失败则返回 FALSE。
In PHP versions before 5.0.0 you must use ocicancel() instead. This name still can be used, it was left as alias of oci_cancel() for downwards compatability. This, however, is deprecated and not recommended.