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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