Obtains a number guaranteed to be unique for the given
relation and will pass it back in the variable
given as uniqueid.
DBPLUS_ERR_NOERR on success or a db++ error
code on failure.
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.