限制的Cypher查询

Question

我目前使用的有50000个节点和200万间关系的Neo4j的数据库进行暗号MATCH查询，像下面这样：

start startnode = node(42660), endnode = node(30561) 
match startnode-[r*1..3]->endnode 
return r; 

此查询本身提供了443行，但我只想要Cypher找到5个匹配并仅返回这些匹配。请允许我澄清：我不仅仅希望Cypher只返回5个结果，我还希望密码一旦找到5个结果就停止查询。我不希望Cypher得到所有443结果。

这是目前使用LIMIT子句吗？或者LIMIT等待所有443个结果被发现，那么只返回前5个？

编辑：LIMIT子句是否会找到像这样的复杂查询的前几个结果？

start graphnode = node(1), startnode = node(42660), endnode = node(30561) 
match startnode<-[:CONTAINS]-graphnode-[:CONTAINS]->endnode 
with startnode, endnode 
match startnode-[r1*1..1]->endnode 
with r1, startnode, endnode 
limit 30 
match startnode-[r2*2..2]->endnode 
with r1, r2, startnode, endnode 
limit 30 
match startnode-[r3*3..3]->endnode 
with r1, r2, r3, startnode, endnode 
limit 30 
return r1,r2,r3; 

这里是profile为查询：

==> ColumnFilter(symKeys=[" UNNAMED216", "endnode", "r1", "startnode", "r2", "r3"], returnItemNames=["r1", "r2", "r3"], _rows=30, _db_hits=0) 
==> Slice(limit="Literal(30)", _rows=30, _db_hits=0) 
==> PatternMatch(g="(startnode)-[' UNNAMED216']-(endnode)", _rows=30, _db_hits=0) 
==>  ColumnFilter(symKeys=["endnode", " UNNAMED140", "r1", "startnode", "r2"], returnItemNames=["r1", "r2", "startnode", "endnode"], _rows=1, _db_hits=0) 
==>  Slice(limit="Literal(30)", _rows=1, _db_hits=0) 
==>   PatternMatch(g="(startnode)-[' UNNAMED140']-(endnode)", _rows=1, _db_hits=0) 
==>   ColumnFilter(symKeys=["startnode", "endnode", " UNNAMED68", "r1"], returnItemNames=["r1", "startnode", "endnode"], _rows=1, _db_hits=0) 
==>    Slice(limit="Literal(30)", _rows=1, _db_hits=0) 
==>    PatternMatch(g="(startnode)-[' UNNAMED68']-(endnode)", _rows=1, _db_hits=0) 
==>     NodeById(name="Literal(List(30561))", identifier="endnode", _rows=1, _db_hits=1) 
==>     NodeById(name="Literal(List(42660))", identifier="startnode", _rows=1, _db_hits=1) 

Answer 1

这取决于你在做什么，但在这种情况下，如果你是return后添加limit 5，就能够懒洋洋地返回并跳过其余的比赛。如果你想要排序或聚合，它将无法为你做到这一点。如果你觉得这不是问题，请将其报告为GitHub上的问题

更新新的查询

start graphnode = node(1), startnode = node(42660), endnode = node(30561) 
match startnode<-[:CONTAINS]-graphnode-[:CONTAINS]->endnode // do you need this, or is it always going to be true? 
with startnode, endnode          // ditto. take it out if it doesn't need to be here. 
match startnode-[r1*1..1]->endnode // this can probably be simplified to just startnode-[r1]->endnode 
with r1, startnode, endnode 
limit 30 // limit to the first 30 it finds in the previous match (this should be lazy) 
match startnode-[r2*2..2]->endnode // finds 2 levels deep 
with r1, r2, startnode, endnode 
limit 30 // limit to the first 30 it finds in the previous match (this should be lazy) 
match startnode-[r3*3..3]->endnode 
return r1,r2,r3 // the last with you had was extraneous, return will function the same way 
limit 30; 

所以（与你正在使用的版本等一起）我假设你问一个问题，因为这个查询很慢。我可以问你为什么这样分手，而不仅仅是startnode-[r*1..3]->endnode和limit 30？你真的需要第一场比赛吗？或者这种检查是不必要的？你能提供PROFILE的输出吗？