gregfelice opened a new pull request, #2444:
URL: https://github.com/apache/age/pull/2444
## Problem
A single-node labeled pattern used as a boolean expression — e.g. `WHERE
(a:Person)` or `WHERE EXISTS((a:Person))` — is accepted but does **not** test
the bound vertex's label. It evaluates as trivially true, so the predicate
matches every row.
Repro (on `master`):
```sql
SELECT * FROM cypher('g', $$ CREATE (:Person {name:'Alice'}), (:Animal
{name:'Rex'}) $$) AS (r agtype);
-- returns BOTH Alice and Rex; should return only Alice
SELECT * FROM cypher('g', $$ MATCH (a) WHERE (a:Person) RETURN a.name $$) AS
(n agtype);
```
## Root cause
A single-node pattern expression desugars to an `EXISTS` sub-pattern.
`make_path_join_quals()` returns early for vertex-only patterns
(`list_length(entities) < 3`), emitting no quals. With no edge to carry a
correlation, the sub-pattern references nothing from the enclosing query, so
the planner produces an **uncorrelated one-time InitPlan** that is true
whenever any vertex of that label exists — independent of the outer row.
Relationship patterns are unaffected: the edge-driven join (`start_id =
a.id`) correlates them to the outer variable, which is why `WHERE
(a)-[:R]->(b)` works correctly.
`EXPLAIN` before the fix — uncorrelated `InitPlan` with a `One-Time Filter`:
```
InitPlan 1
-> Result
One-Time Filter: ((InitPlan 1).col1)::agtype
```
After the fix — correlated `SubPlan` referencing the outer `a_1`:
```
SubPlan 1
-> Result
One-Time Filter: ((_extract_label_id(a_1.id))::integer = 3)
```
## Fix
In `make_path_join_quals()`, for a vertex-only pattern whose vertex carries
a non-default label **and** whose variable is declared in an ancestor parse
state (a correlated reference), emit an explicit label-id filter. `make_qual()`
builds a name-based id reference that resolves to the outer variable, so the
filter both **correlates** the sub-pattern to that variable and **enforces**
the label.
Freshly scanned, non-correlated vertices (no ancestor binding) are
untouched, so `MATCH (a:Person)` and "does any X exist" `EXISTS` checks behave
exactly as before.
## Testing
Added regression coverage to `pattern_expression` against a graph containing
a non-`Person` vertex:
- `WHERE (a:Person)` → only the `:Person` vertices
- `WHERE NOT (a:Person)` → only the non-`Person` vertex
- `WHERE EXISTS((a:Company))` → only the `:Company` vertex
All 41 regression tests pass (`make installcheck`).
## Note
`RETURN (a:Label)` in a **projection** on an unlabeled bound variable still
errors with "multiple labels for variable" — that is a separate, pre-existing
guard, orthogonal to this fix, and is intentionally left unchanged.
Fixes #2443
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