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Pushdown DISTINCT agg fields as (additional) GROUP BY keys #24

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kaikalur opened this issue Mar 20, 2022 · 0 comments

kaikalur commented Mar 20, 2022 •

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DISTINCT aggs like COUNT DISTINCT are expensive. But in most cases it is helpful to push down these as group by keys before counting them.

SELECT agg(x), COUNT(DISTINCT y) FROM T GROUP BY z;

can be rewritten as

SELECT agg(x), COUNT(DISTINCT y) FROM (SELECT partial_agg(x) AS x, y, z FROM T GROUP BY y, z) AS T GROUP BY z;

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