avg_state ​

avg_state returns an intermediate average state. It retains a total and count rather than only the average, so a later merge can combine batches with the correct weights.

Create typed state storage ​

CREATE TABLE readings(batch UInt8, value Int64);
INSERT INTO readings VALUES (1, 10), (1, 20), (2, 90);
CREATE TABLE partials(batch UInt8, state AggregateFunction(avg, Int64));

Store one state per batch ​

INSERT INTO partials
SELECT batch, avg_state(value)
FROM readings
GROUP BY batch;

Read a state's value ​

finalize_aggregation reads a single state's result:

SELECT batch, finalize_aggregation(state) AS average_value
FROM partials
ORDER BY batch
FORMAT csv;

1,15.0
2,90.0

Use avg_merge to combine several states. State function names and argument types must match the storage declaration exactly; CoordinatorDB states are not compatible with ClickHouse state bytes.