Monotonically Increasing

s-Server streams generally need to increase monotonically by ROWTIME. Some operators require monotonically increasing values; in particular, the streaming GROUP BY operator requires that at least one of its arguments be monotonic and non-constant. Also, if SQLstream can deduce that an expression is monotonically increasing, it may be able to evaluate the the query more efficiently. Using the MONOTONIC function asserts to SQLstream that x is monotonic.