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Posted to github@datafusion.apache.org by "nathanb9 (via GitHub)" <gi...@apache.org> on 2026/06/26 22:35:59 UTC
[I] Fuse multiple scalar-aggregate subqueries over the same source into a single scan [datafusion]
nathanb9 opened a new issue, #23213:
URL: https://github.com/apache/datafusion/issues/23213
**Problem**
When a query computes several uncorrelated scalar-aggregate subqueries over the same table, DataFusion scans that table once per subquery.
**Proposed rewrite**
When 2 or more such subqueries share one source, fuse them into a single scan + aggregate, pushing each subquery's predicate into a `FILTER (WHERE ...)` clause:
```sql
-- Before: two scans of t
SELECT (SELECT count(*) FROM t WHERE a < 10),
(SELECT avg(x) FROM t WHERE a >= 10);
-- After: one scan of t
SELECT count(*) FILTER (WHERE a < 10),
avg(x) FILTER (WHERE a >= 10)
FROM t;
```
The source filter becomes the OR of the branch predicates, and each scalar subquery is replaced by a reference to the merged aggregate.
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Re: [I] Fuse multiple scalar-aggregate subqueries over the same source into a single scan [datafusion]
Posted by "nathanb9 (via GitHub)" <gi...@apache.org>.
nathanb9 commented on issue #23213:
URL: https://github.com/apache/datafusion/issues/23213#issuecomment-4813880905
take
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