Window Aggregates

Individual orders are flowing; now summarize them. A window processor collects records into sliding windows and constructs aggregate output. Declared BRANCHED BY by_customer, it windows each customer independently — building directly on Branched Processing.

The Summary Model

Window routes are set-only: every output field is an aggregate expression, so the output relay needs its own summary schema (the order schema cannot be reused unless every field is aggregated):

BEGIN;

CREATE SCHEMA order_window (
  customer STRING,
  order_count I64,
  total_amount I64,
  max_amount I64,
  avg_amount F64
);

CREATE RELAY order_windows SCHEMA order_window BRANCHED BY by_customer;

The Window Processor

Windows use WIDTH and STEP instead of FLUSH. Each bound can count messages, elapse a duration, or combine both — a combined bound closes the window when either condition is met:

CREATE WINDOW PROCESSOR customer_order_window
  FROM orders_by_customer
  WIDTH 3 MESSAGES 30s DURATION
  STEP 3 MESSAGES 30s DURATION
  BRANCHED BY by_customer
  TO order_windows
    SET customer = FIRST(input.customer),
        order_count = COUNT(input.order_id),
        total_amount = SUM(input.amount),
        max_amount = MAX(input.amount),
        avg_amount = AVG(input.amount)
  ON MESSAGE ERROR LOG;

COMMIT;

• The aggregate functions are COUNT, COUNT_IF, SUM, AVG, MIN, MAX, FIRST, LAST, ARG_MIN, ARG_MAX, BOOL_AND, BOOL_OR, VAR_POP, VAR_SAMP, STDDEV_POP, STDDEV_SAMP, COVAR_POP, COVAR_SAMP, CORR, and PERCENTILE_LINEAR_HISTOGRAM, and the approximate APPROX_COUNT_DISTINCT, APPROX_QUANTILE, and APPROX_TOP_K. Aggregate calls also participate in larger scalar expressions. See Window Aggregates for their types, null handling, numerical behavior, and the bounded state the approximate ones need.
• A null argument contributes nothing to an aggregate. An aggregate that can be null, such as VAR_SAMP or any aggregate over an OPTIONAL field, needs an OPTIONAL output field or a COALESCE.
• input.<field> is valid only inside aggregate arguments; a bare customer = input.customer is rejected. Aggregates cannot be nested.
• WIDTH equal to STEP makes the windows tumbling (no overlap); a smaller STEP slides them. STEP may never exceed WIDTH.
• Every required field of order_window must be assigned, and every SET target must exist in the schema.

Watch The Summaries

nervix-cli --domain quickstart subscribe window_watch order_windows

Produce three acme orders. When the third arrives, one summary record for the acme branch appears — order_count of 3, with the totals. Interleave globex orders and you will see that each customer’s window fills separately: the branch keeps window state per customer, exactly like the deduplicator’s history. If a window stays partially filled, the 30s duration bound closes it.

Duration bounds start from record timestamp watermarks and become due when a later watermark or the bound domain clock reaches the target. A paced domain’s TIME RATE changes the real wait for a partially filled window while preserving the records’ external event timestamps. The output keeps the window’s minimum low watermark and records the emission snapshot as its high watermark. See Ingestion Timestamps.

Next: produce records without any input at all in Generators.