Articles by tag: aggregation

ClickHouse Materialized Views: triggers on INSERT

How MV work in ClickHouse: incremental aggregation, chains minute→hour→day, Null+Kafka pattern, POPULATE and its dangers. Examples with SummingMergeTree and AggregatingMergeTree.

CollapsingMergeTree in ClickHouse: update without UPDATE

How CollapsingMergeTree and VersionedCollapsingMergeTree replace UPDATE in ClickHouse: sign column, collapsing pairs, SUM(amount*sign), ordering problem and solution via versions.

SummingMergeTree and AggregatingMergeTree in ClickHouse

Incremental aggregation in ClickHouse: how SummingMergeTree and AggregatingMergeTree speed up dashboards by 100 times. Examples, materialized views, pitfalls, and comparison.