如何将四个Neo4j GraphDB查询合并为单个查询并获取结果？

问题原因 #

你之前尝试在ATTACHED_TO后同时指定Department、Section、Images标签，这种写法要求找到同时属于这三个标签的节点——显然不存在这类节点，所以返回空结果。

正确合并方案 #

方案一：用OPTIONAL MATCH分别匹配各类关联节点

这种方式能保证即使某类节点不存在，其他类型的结果仍能正常返回：

MATCH (n:Companies{company_id:1})
OPTIONAL MATCH (n)-[:ATTACHED_TO]-(t:Department)
OPTIONAL MATCH (n)-[:ATTACHED_TO]-(c:Section)
OPTIONAL MATCH (n)-[:ATTACHED_TO]-(g:Images)
RETURN
  n AS company,
  collect(DISTINCT t) AS departments,
  collect(DISTINCT c) AS sections,
  collect(DISTINCT g) AS images

方案二：匹配所有关联节点后按标签分类收集

如果想减少匹配语句数量，可以先匹配所有关联节点，再通过标签判断分类：

MATCH (n:Companies{company_id:1})
OPTIONAL MATCH (n)-[:ATTACHED_TO]-(t)
WHERE t:Department OR t:Section OR t:Images
WITH n, t, labels(t) AS nodeLabels
RETURN
  n AS company,
  collect(DISTINCT CASE WHEN 'Department' IN nodeLabels THEN t END) AS departments,
  collect(DISTINCT CASE WHEN 'Section' IN nodeLabels THEN t END) AS sections,
  collect(DISTINCT CASE WHEN 'Images' IN nodeLabels THEN t END) AS images

内容的提问来源于stack exchange，提问作者Narayan bhat