Warning: This function is
EXPERIMENTAL. The behaviour of this function, the
name of this function, and anything else documented about this
function may change without notice in a future release of PHP.
Use this function at your own risk.
Returns the cause of this exception or NULL if the cause is nonexistent or unknown.
Typically the cause will be an SDO_CPPException object, which may
be used to obtain additional diagnostic information.
Return Values
Returns the cause of this exception or NULL if the cause is nonexistent or unknown.