Maksim Zhuravkov created IGNITE-20009:
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Summary: Sql. Rework 2-phase aggregates part 2. AVG as SUM / COUNT.
Key: IGNITE-20009
URL: https://issues.apache.org/jira/browse/IGNITE-20009
Project: Ignite
Issue Type: Improvement
Components: sql
Affects Versions: 3.0.0-beta1
Reporter: Maksim Zhuravkov
Map/reduce implementation of some aggregates requires replacing an aggregate
with a combination of aggregates. For example AVG(x) should be implemented as :
MAP: SUM(x) sum_x, COUNT (x) as count_x
REDUCE: SUM(sum_x)/SUM(COUNT(count_x))
To implement this we need the following changes:
- Replace AVG on MAP phase with SUM and COUNT.
- Change rowType produced by MAP phase/accepted by REDUCE phase.
- Add a projection after reduce aggregate that includes division and produces
final result (it obviously should include other aggregation results as well in
the correct order).
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