MuhammadTahaNaveed opened a new pull request, #2406:
URL: https://github.com/apache/age/pull/2406
Two related defects in how AGE handled cypher null inside list-iterating
constructs.
age_unnest packaged every iterated element as a non-SQL-NULL agtype datum,
even AGTV_NULL scalars. SQL `IS NULL` / `IS NOT NULL` then couldn't see those
nulls, so `[x IN [null, 1] WHERE x IS NULL]` dropped the null it was meant to
keep, and `WHERE x IS NOT NULL` kept the null it was meant to drop. The same
mismatch surfaced in UNWIND. AGE already treats SQL NULL as the row-level
representation of cypher null elsewhere (`RETURN null AS v` yields SQL NULL,
strict operators short-circuit on it); age_unnest now does the same by emitting
the row with `nulls[0] = true` when the element is AGTV_NULL.
single() previously transformed to `SELECT count(*) FROM unnest(list) AS x
WHERE pred IS TRUE`, with the grammar wrapping the result as `(subquery) = 1`.
With the unnest fix, `[null, 5] WHERE x > 0` left one definite true after the
WHERE filter -> count = 1 -> true. Neo4j returns null because the unknown
predicate could itself be a second match. Rewritten to a CASE built on
`count(*) FILTER (WHERE pred IS TRUE)` and `bool_or(pred IS NULL)`:
CASE WHEN count(*) FILTER (WHERE pred IS TRUE) >= 2 THEN false
WHEN bool_or(pred IS NULL) THEN NULL
WHEN count(*) FILTER (WHERE pred IS TRUE) = 1 THEN true
ELSE false END
The >=2 arm runs first so two definite trues dominate any unknowns. Fits
inside the existing make_predicate_case_expr helper alongside all/any/none,
removes the special-case transform branch and the grammar `= 1` wrap. A small
`make_count_star_filter_agg` helper mirrors the existing `make_bool_or_agg`.
Verified against Neo4j for the new edge cases (one-true-plus-null,
two-trues-plus-null, all-nulls, mixed-true-false-null).
The predicate_functions regression also picks up the corrected behavior of
any/all/none over null elements: `null > 0` now yields SQL NULL instead of
being silently treated as true, so the three-valued combinators in those
functions produce the openCypher results the comments previously documented as
buggy.
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