我试图识别只有一种给定类型关系的节点。
想象一下Route和Stop节点的图表。路由可能有0个或多个停止，多个路由之间可以共享停止，停止必须始终至少有1个路由。我想匹配并删除在删除给定路由时将成为孤立的停止。
在任何人说什么之前，我知道在删除路线之后找到没有路线的站点会更容易，但这不是一个选项。我们也不担心在这里删除路线，只是停靠。
这是我的疑问：
MATCH (r1:Route { id: {route_id} })-[rel1:HAS_STOP]->(s:Stop)
MATCH (r2:Route)-[rel2:HAS_STOP]->(s)
WITH s, COUNT(rel2) as c
WHERE c = 1
MATCH s-[rel2]-()
DELETE s, rel2
这完美无缺......但有更好的方法吗？感觉它可能更有效但我不确定如何。
答案 0 :(得分：2)
修改
此处的查询仅匹配将在不删除当前路由的情况下成为孤立的节点：
MATCH (route:Route {id:'99e08bdf-130f-3fca-8292-27d616fa025f'})
WITH route
OPTIONAL MATCH (route)-[r:HAS_STOP]->(s)
WHERE NOT EXISTS((route)--(s)<-[:HAS_STOP]-())
DELETE r,s
和执行计划：
neo4j-sh (?)$ PROFILE MATCH (route:Route {id:'99e08bdf-130f-3fca-8292-27d616fa025f'})
> WITH route
> OPTIONAL MATCH (route)-[r:HAS_STOP]->(s)
> WHERE NOT EXISTS((route)--(s)<-[:HAS_STOP]-())
> DELETE r,s;
+-------------------+
| No data returned. |
+-------------------+
Nodes deleted: 2
Relationships deleted: 2
EmptyResult
|
+UpdateGraph
|
+Eager
|
+OptionalMatch
|
+SchemaIndex(1)
|
+Filter
|
+SimplePatternMatcher
|
+SchemaIndex(1)
+----------------------+------+--------+--------------+----------------------------------------------------------------------------------------------------+
| Operator | Rows | DbHits | Identifiers | Other |
+----------------------+------+--------+--------------+----------------------------------------------------------------------------------------------------+
| EmptyResult | 0 | 0 | | |
| UpdateGraph | 2 | 4 | | DeleteEntity; DeleteEntity |
| Eager | 2 | 0 | | |
| OptionalMatch | 2 | 0 | | |
| SchemaIndex(1) | 1 | 2 | route, route | { AUTOSTRING0}; :Route(id) |
| Filter | 2 | 0 | | NOT(nonEmpty(PathExpression((route)-[ UNNAMED140]-(s),(160)-[ UNNAMED145:HAS_STOP]->(s), true))) |
| SimplePatternMatcher | 2 | 0 | route, s, r | |
| SchemaIndex(1) | 1 | 2 | route, route | { AUTOSTRING0}; :Route(id) |
+----------------------+------+--------+--------------+----------------------------------------------------------------------------------------------------+
Total database accesses: 8
** OLD ANSWER **
我让它在这里帮助别人：
在您的查询中，您不会删除路线，也不会删除不会孤立的停靠点的关系。你可以一气呵成。
这就是我查询相同用例的方法，我还比较了测试图上的两个执行计划，每个路由有大约160个停止点和2个停止位置，在删除路由后将成为孤立的，图形可在此处获取：http://graphgen.neoxygen.io/?graph=JPnvQWZcQW685m
我的查询：
MATCH (route:Route {id:'e70ea0d4-03e2-3ca4-afc0-dfdc1754868e'})
WITH route
MATCH (route)-[r:HAS_STOP]->(s)
WITH r, collect(s) as stops
DELETE r, route
WITH filter(x in stops WHERE NOT x--()) as orphans
UNWIND orphans as orphan
DELETE orphan
这是我的个人资料查询：
neo4j-sh (?)$ PROFILE MATCH (route:Route {id:'1c565ac4-b72b-37c3-be7f-a38f2a7f66a8'})
> WITH route
> MATCH (route)-[r:HAS_STOP]->(s)
> WITH route, r, collect(s) as stops
> DELETE r, route
> WITH filter(x in stops WHERE NOT x--()) as orphans
> UNWIND orphans as orphan
> DELETE orphan;
+-------------------+
| No data returned. |
+-------------------+
Nodes deleted: 2
Relationships deleted: 157
EmptyResult
|
+UpdateGraph(0)
|
+UNWIND
|
+ColumnFilter(0)
|
+Eager
|
+Extract
|
+UpdateGraph(1)
|
+ColumnFilter(1)
|
+EagerAggregation
|
+SimplePatternMatcher
|
+SchemaIndex
+----------------------+------+--------+--------------+------------------------------+
| Operator | Rows | DbHits | Identifiers | Other |
+----------------------+------+--------+--------------+------------------------------+
| EmptyResult | 0 | 0 | | |
| UpdateGraph(0) | 1 | 1 | | DeleteEntity |
| UNWIND | 1 | 0 | | |
| ColumnFilter(0) | 157 | 0 | | keep columns orphans |
| Eager | 157 | 0 | | |
| Extract | 157 | 0 | | orphans |
| UpdateGraph(1) | 157 | 158 | | DeleteEntity; DeleteEntity |
| ColumnFilter(1) | 157 | 0 | | keep columns route, r, stops |
| EagerAggregation | 157 | 0 | | route, r |
| SimplePatternMatcher | 157 | 0 | route, s, r | |
| SchemaIndex | 1 | 2 | route, route | { AUTOSTRING0}; :Route(id) |
+----------------------+------+--------+--------------+------------------------------+
Total database accesses: 161
使用您的查询：
我稍微修改了您的查询以使用模式索引
这是您查询的执行计划，数据库访问的差异非常大
PROFILE MATCH (r1:Route { id: '1c565ac4-b72b-37c3-be7f-a38f2a7f66a8' })
> WITH r1
> MATCH (r1)-[rel1:HAS_STOP]->(s:Stop)
> MATCH (r2:Route)-[rel2:HAS_STOP]->(s)
> WITH s, COUNT(rel2) as c
> WHERE c = 1
> MATCH s-[rel2]-()
> DELETE s, rel2;
+-------------------+
| No data returned. |
+-------------------+
Nodes deleted: 1
Relationships deleted: 1
EmptyResult
|
+UpdateGraph
|
+Eager
|
+SimplePatternMatcher(0)
|
+Filter(0)
|
+ColumnFilter
|
+EagerAggregation
|
+Filter(1)
|
+SimplePatternMatcher(1)
|
+Filter(2)
|
+SimplePatternMatcher(2)
|
+SchemaIndex
+-------------------------+------+--------+-----------------------+-----------------------------+
| Operator | Rows | DbHits | Identifiers | Other |
+-------------------------+------+--------+-----------------------+-----------------------------+
| EmptyResult | 0 | 0 | | |
| UpdateGraph | 1 | 2 | | DeleteEntity; DeleteEntity |
| Eager | 1 | 0 | | |
| SimplePatternMatcher(0) | 1 | 0 | UNNAMED200, s, rel2 | |
| Filter(0) | 1 | 0 | | c == { AUTOINT1} |
| ColumnFilter | 157 | 0 | | keep columns s, c |
| EagerAggregation | 157 | 0 | | s |
| Filter(1) | 4797 | 4797 | | hasLabel(r2:Route(4)) |
| SimplePatternMatcher(1) | 4797 | 4797 | r2, s, rel2 | |
| Filter(2) | 157 | 157 | | hasLabel(s:Stop(3)) |
| SimplePatternMatcher(2) | 157 | 157 | r1, s, rel1 | |
| SchemaIndex | 1 | 2 | r1, r1 | { AUTOSTRING0}; :Route(id) |
+-------------------------+------+--------+-----------------------+-----------------------------+
Total database accesses: 9912