neo4j - CASE 语句中的测试变量 "not defined"

Question

我觉得试图让一个基本的 CASE 陈述栩栩如生:

MATCH (n)
WITH id(n)%2 as r,
    CASE r 
        WHEN 1 THEN "odd" 
        WHEN 0 THEN "even" 
    END AS result
RETURN result

我得到的错误是“变量 r 未定义”。我已经尝试了几乎所有的东西。我不是在解决任何其他问题，而是让 CASE 语句用于教育目的。

Answer 1

尝试:

MATCH (n)
WITH id(n)%2 AS r
RETURN CASE r WHEN 1 THEN "odd" WHEN 0 THEN "even" END AS result

您必须首先将 r 定义为变量，然后您才能在下一个 WITH/RETURN 子句中使用它.请参阅有关 variables 范围的文档:

Variables are not carried over to subsequent queries. If multiple query parts are chained together using WITH, variables have to be listed in the WITH clause to be carried over to the next part.

更新，基于@logisima 的评论。您甚至可以省略整个 WITH:

MATCH (n)
RETURN CASE id(n)%2 WHEN 1 THEN 'odd' WHEN 0 THEN 'even' END AS result