Neo4j Cypher query empty collect使整个结果为空

我一直面临wierd问题，我试图从我构建的neo4j图中获取数据

MATCH (u1:User {user_id: 4})-[:FOLLOWS]->(u2:User)-[]->(r1:Rest{city_id: 1})
WITH COLLECT ({ REST: r1.res_id}) as rows
MATCH (u1:User {user_id: 4})-[rel]->(r2:Rest{city_id: 1})
WHERE NOT (u1:User {user_id: 4})-[rel : BEEN_THERE | ADD_REVIEW]->(r2:Rest{city_id: 1})
WITH rows + COLLECT ({ REST: r2.res_id}) AS allrows
UNWIND allrows as row 
RETURN row.REST as RESTAURANT_ID, count(row.REST) as COUNT
ORDER BY COUNT desc
LIMIT 15;

---

但是，当COLLECT（{REST:r2.res_id}）的结果为空时，整个结果将变为空。此外，查询无法从第一次匹配中识别行并返回未定义的

行

。请让我知道。谢谢

如果模式与任何路径都不匹配，则结果将确实为空

您必须将

匹配

拆分为2，并将第二个

设置为可选

，或者在实际情况中，反复停止匹配相同的

u1

节点：

MATCH (u1:User {user_id: 4})
OPTIONAL MATCH (u1)-[:FOLLOWS]->(:User)-->(r1:Rest {city_id: 1})
WITH u1, collect({ REST: r1.res_id }) AS rows
OPTIONAL MATCH (u1)-->(r2:Rest {city_id: 1})
WHERE NOT (u1)-[:BEEN_THERE | ADD_REVIEW]->(r2)
WITH rows + collect({ REST: r2.res_id }) AS allrows
UNWIND allrows as row 
RETURN row.REST AS RESTAURANT_ID, count(row.REST) AS COUNT
ORDER BY COUNT desc
LIMIT 15

---

我不确定第一个

可选匹配

（您只提到第二个

collect

是一个拦截器），但如果您希望两个模式的聚合，其中每个模式都可以为空，那就来吧。

非常感谢您的回答！它工作正常。@AditKaushal请毫不犹豫地回答。