Inconsistent Behavior of GROUP BY ROLLUP in v17 vs master

邱宇航 <iamqyh@gmail.com>

From: 邱宇航 <iamqyh@gmail.com>

To: PostgreSQL-development <pgsql-hackers@postgresql.org>

Date: 2025-09-23T03:48:58Z

Lists: pgsql-hackers

Commits

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Fix test case from 40c242830
- ee49f2cf447a 18.1 landed
Fix pushdown of degenerate HAVING clauses
- 40c2428307b8 18.1 landed
- 18d261409348 19 (unreleased) landed
Allow pushdown of HAVING clauses with grouping sets
- 67a54b9e83d3 18.0 cited
Mark expressions nullable by grouping sets
- f5050f795aea 18.0 cited

I've noticed that two GROUP BY ROLLUP queries behave differently in v17
compared to master and REL_18_STABLE. The issue can be reproduced by
following SQL:

``` SQL
CREATE TABLE t(id int);

INSERT INTO t SELECT generate_series(1, 3);

-- Query 1
SELECT DISTINCT 'XXX'
FROM t
GROUP BY ROLLUP (id, 1);

-- Query 2
SELECT 'XXX'
FROM t
GROUP BY ROLLUP(id)
HAVING NOT (NULL IS NULL);
```

After some git bisect work, I traced the root cause:
- The first issue was introduced by commit f5050f79 (Mark expressions
nullable by grouping sets).
- The second issue stems from commit 67a54b9e (Allow pushdown of HAVING
clauses with grouping sets).

Best regards,
Yuhang Qiu