Re: BUG #18252: Assert in CheckOpSlotCompatibility() fails when recursive union filters tuples in non-recursive term

On Tue, Dec 19, 2023 at 12:30 AM PG Bug reporting form <noreply@postgresql.org> wrote:

CREATE TABLE t(i int);
INSERT INTO t VALUES (1), (1);

WITH RECURSIVE rt(i) AS (
    SELECT * FROM t
    UNION
    SELECT * FROM rt
)
SELECT * FROM rt;

Nice catch.  The TupleHashTable's tableslot is created as type
TTSOpsMinimalTuple.  The RecursiveUnion's non-recursive term generates
tuples of type TTSOpsBufferHeapTuple.  If the non-recursive term
produces duplicate tuples, we'd find non-empty bucket when inserting the
same key into the hashtable.  In this case we need to check to see if
the two tuples match: one is of the hashtable's tableslot
(TTSOpsMinimalTuple), and the other comes from the non-recursive term
(TTSOpsBufferHeapTuple).  And the incompatible slot type would fail
CheckOpSlotCompatibility.