Cypher含DISTINCT的RETURN语句无法排序问题求助

问题场景 #

执行以下Cypher查询时触发错误：

WITH $arrayHere as ids
UNWIND ids as id
MATCH(o:`App`)-[:ContainsFood]->(d:Food:`App`) WHERE id(o) = id
RETURN DISTINCT {Document: d} ORDER BY d.Title

错误信息 #

In a WITH/RETURN with DISTINCT or an aggregation, it is not possible to access variables declared before the WITH/RETURN: d (line 5, column 42 (offset: 308))
" RETURN DISTINCT {Food: d} ORDER BY d.Title"

解决办法 #

调整查询逻辑，先通过WITH DISTINCT对d进行去重并保留变量，再执行返回和排序：

WITH $arrayHere as ids
UNWIND ids as id
MATCH(o:`App`)-[:ContainsFood]->(d:Food:`App`) WHERE id(o) = id
WITH DISTINCT d
RETURN {Document: d} ORDER BY d.Title

原因说明 #

原查询中，RETURN DISTINCT {Document: d}会生成新的映射对象，此时原始变量d已不在当前作用域内，导致ORDER BY d.Title无法访问该变量。通过WITH DISTINCT d提前完成去重并保留d变量，后续的RETURN和ORDER BY就能正常访问d的属性，既实现去重又完成排序需求。

内容的提问来源于stack exchange，提问作者rohit bumrah