Match statement hanging edge problem

[czpmango]

Inconsistent handling of dangling edges leads to incorrect results.

Environments
nebula 3.x

How To Reproduce

(root@nebula) [nba]> insert edge like() values "Tim Duncan"->"emptyPoint":()
Execution succeeded (time spent 2049/2361 us)

(root@nebula) [nba]> go from "Tim Duncan" over like yield like._dst,$$.player.age
+-----------------+---------------+
| like._dst       | $$.player.age |
+-----------------+---------------+
| "Manu Ginobili" | 41            |
| "Tony Parker"   | 36            |
| "emptyPoint"    | __NULL__      |
+-----------------+---------------+
Got 3 rows (time spent 3504/3903 us)

(root@nebula) [nba]> match (v)-[:like]->(n) where id(v)=="Tim Duncan" return v
+-------------------------------------------------------------------------------------------------------------+
| v                                                                                                           |
+-------------------------------------------------------------------------------------------------------------+
| ("Tim Duncan" :player{age: 42, name: "Tim Duncan"} :bachelor{name: "Tim Duncan", speciality: "psychology"}) |
| ("Tim Duncan" :player{age: 42, name: "Tim Duncan"} :bachelor{name: "Tim Duncan", speciality: "psychology"}) |
+-------------------------------------------------------------------------------------------------------------+
Got 2 rows (time spent 5232/5640 us)

(root@nebula) [nba]> match (v)-[:like]->() where id(v)=="Tim Duncan" return v
+-------------------------------------------------------------------------------------------------------------+
| v                                                                                                           |
+-------------------------------------------------------------------------------------------------------------+
| ("Tim Duncan" :player{age: 42, name: "Tim Duncan"} :bachelor{name: "Tim Duncan", speciality: "psychology"}) |
| ("Tim Duncan" :player{age: 42, name: "Tim Duncan"} :bachelor{name: "Tim Duncan", speciality: "psychology"}) |
| ("Tim Duncan" :player{age: 42, name: "Tim Duncan"} :bachelor{name: "Tim Duncan", speciality: "psychology"}) |
+-------------------------------------------------------------------------------------------------------------+
Got 3 rows (time spent 3606/4029 us)

Expected behavior
Query behave consistently for dangling edges.

[Sophie-Xie]

Discuss it offline: 3.x will not fix it.

[shanlai]

(root@nebula) [nba]> INSERT VERTEX player(name, age) VALUES "close_tagless_5":("close_tagless_5", 18),"close_tagless_6":("close_tagless_6", 18);
Execution succeeded (time spent 1627/70852 us)

(root@nebula) [nba]> INSERT EDGE follow () VALUES "close_tagless_5"->"close_tagless_6":()
Execution succeeded (time spent 1744/62764 us)

(root@nebula) [nba]> delete vertex "close_tagless_5"
Execution succeeded (time spent 2013/78905 us)

(root@nebula) [nba]> match (v)-[e:follow]->(v1) where id(v)=="close_tagless_5" return v,e
+---------------------+----------------------------------------------------------------------+
| v                   | e                                                                    |
+---------------------+----------------------------------------------------------------------+
| ("close_tagless_5") | [:follow "close_tagless_5"->"close_tagless_6" @0 {degree: __NULL__}] |
+---------------------+----------------------------------------------------------------------+
Got 1 rows (time spent 2640/64082 us)

(root@nebula) [nba]> match (v)<-[e:follow]-(v1) where id(v)=="close_tagless_6" return v,e
+---+---+
| v | e |
+---+---+
+---+---+
Empty set (time spent 2729/68645 us)

Expected behavior
Query behave consistently for dangling edges.

[wey-gu]

Shall we consider adding an option(like if vertex exists) in the insert edge to ensure the user won't introduce hanging edges unwillingly?

@MuYiYong

[czpmango]

I don't have the context for your offline discussion. But IMHO, this issue should be reopened.
Another point to consider is that AppendVertices operator will bring some performance overhead when there is no need to get vertex properties.

[czpmango]

In addition, it will cause correctness problems. For example, this optimizer rule called PushLimitDownScanAppendVerticesRule is not valid.