Neo4j简单`CASE`表达

Question

我正在尝试使用neo4j CASE构造生成一个表，其中包含发件人的名称，接收者的名称以及发件人作为计数发送的消息数（如果有的话，否则为0）但我我没有得到预期的结果。这是我的疑问：

MATCH(e:Employee{key:1}),(b:Employee), 
OPTIONAL MATCH (e)-[r:Message]->(b)
RETURN e.name, DISTINCT b.name,
CASE
WHEN (e)-[r:Message]->(b)
THEN COUNT(r)
ELSE 0 END AS Messages

我在这里做错了什么？提前谢谢！

Answer 1

I believe you do not need this CASE WHEN to achieve your goal. If you need the count() of :Message relationships between e and b nodes you can simply return the count of it:

MATCH(e:Employee{key:1}),(b:Employee)
OPTIONAL MATCH (e)-[r:Message]->(b)
RETURN DISTINCT e.name, b.name, COUNT(r) as Messages

This query will return zero in the COUNT(r) if no relationship exists between e and b nodes.