我从一个csv文件导入了数据并创建了许多节点，所有节点都与同一数据集中基于“树编号”层次结构系统的其他节点相关：
例如，树编号为a01.111的节点是节点a01的直接子节点，树编号为a01.111.230的节点是节点a01.111的直接子节点。
我要做的是在节点之间创建唯一的关系，这些节点是其他节点的直接子节点。例如，节点a01.111.230应该只有一个与节点a01.111的“is_child_of”关系。
我尝试过几件事，例如：
MATCH (n:Node), (n2:Node)
WHERE (n2.treeNumber STARTS WITH n.treeNumber)
AND (n <> n2)
AND NOT ((n2)-[:IS_CHILD_OF]->())
CREATE UNIQUE (n2)-[:IS_CHILD_OF]->(n);
此示例导致创建唯一的“is-child-of”关系，但不创建与节点的直接父节点的关系。相反，节点a01.111.230将与节点a01相关。
最佳答案
我想建议另一个通用的解决方案，也就是避免像@inversefalcon指出的那样使用笛卡尔积。
我们首先创建一个索引，以便更快地查找，然后插入一些测试数据：
CREATE CONSTRAINT ON (n:Node) ASSERT n.treeNumber IS UNIQUE;
CREATE (n:Node {treeNumber: 'A01.111.230'})
CREATE (n:Node {treeNumber: 'A01.111'})
CREATE (n:Node {treeNumber: 'A01'})
然后我们需要扫描所有节点作为潜在的父节点，并查找以父节点的
treeNumber开始（STARTS WITH可以使用索引）并且在treeNumber的“余数”中没有点（即直接子节点）的子节点，而不是拆分、连接等：MATCH (p:Node), (c:Node)
WHERE c.treeNumber STARTS WITH p.treeNumber
AND p <> c
AND NOT substring(c.treeNumber, length(p.treeNumber) + 1) CONTAINS '.'
RETURN p, c
为了分析的目的，我用一个简单的
RETURN替换了关系的创建，但是您可以用CREATE UNIQUE或MERGE替换它。实际上，我们可以通过预先计算应该匹配的实际前缀来去掉
p <> c谓词和长度上的+ 1：MATCH (p:Node)
WITH p, p.treeNumber + '.' AS parentNumber
MATCH (c:Node)
WHERE c.treeNumber STARTS WITH parentNumber
AND NOT substring(c.treeNumber, length(parentNumber)) CONTAINS '.'
RETURN p, c
但是，分析该查询表明没有使用索引，并且存在笛卡尔积（因此我们有一个o（n^2）算法）：
Compiler CYPHER 3.0
Planner COST
Runtime INTERPRETED
+--------------------+----------------+------+---------+----------------------+------------------------------------------------------------------------------------------------------------------------------------+
| Operator | Estimated Rows | Rows | DB Hits | Variables | Other |
+--------------------+----------------+------+---------+----------------------+------------------------------------------------------------------------------------------------------------------------------------+
| +ProduceResults | 2 | 2 | 0 | c, p | p, c |
| | +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------------------------------------------------+
| +Filter | 2 | 2 | 26 | c, p, parentNumber | NOT(Contains(SubstringFunction(c.treeNumber,length(parentNumber),None),{ AUTOSTRING1})) AND StartsWith(c.treeNumber,parentNumber) |
| | +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------------------------------------------------+
| +Apply | 2 | 9 | 0 | p, parentNumber -- c | |
| |\ +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------------------------------------------------+
| | +NodeByLabelScan | 9 | 9 | 12 | c | :Node |
| | +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------------------------------------------------+
| +Projection | 3 | 3 | 3 | parentNumber -- p | p; Add(p.treeNumber,{ AUTOSTRING0}) |
| | +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------------------------------------------------+
| +NodeByLabelScan | 3 | 3 | 4 | p | :Node |
+--------------------+----------------+------+---------+----------------------+------------------------------------------------------------------------------------------------------------------------------------+
Total database accesses: 45
但是，如果我们简单地添加这样的提示
MATCH (p:Node)
WITH p, p.treeNumber + '.' AS parentNumber
MATCH (c:Node)
USING INDEX c:Node(treeNumber)
WHERE c.treeNumber STARTS WITH parentNumber
AND NOT substring(c.treeNumber, length(parentNumber)) CONTAINS '.'
RETURN p, c
它确实使用索引，我们有类似于o（n*log（n））算法（log（n）用于索引查找）：
Compiler CYPHER 3.0
Planner COST
Runtime INTERPRETED
+-------------------------------+----------------+------+---------+----------------------+------------------------------------------------------------------------------------------+
| Operator | Estimated Rows | Rows | DB Hits | Variables | Other |
+-------------------------------+----------------+------+---------+----------------------+------------------------------------------------------------------------------------------+
| +ProduceResults | 2 | 2 | 0 | c, p | p, c |
| | +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------+
| +Filter | 2 | 2 | 6 | c, p, parentNumber | NOT(Contains(SubstringFunction(c.treeNumber,length(parentNumber),None),{ AUTOSTRING1})) |
| | +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------+
| +Apply | 2 | 3 | 0 | p, parentNumber -- c | |
| |\ +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------+
| | +NodeUniqueIndexSeekByRange | 9 | 3 | 6 | c | :Node(treeNumber STARTS WITH parentNumber) |
| | +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------+
| +Projection | 3 | 3 | 3 | parentNumber -- p | p; Add(p.treeNumber,{ AUTOSTRING0}) |
| | +----------------+------+---------+----------------------+------------------------------------------------------------------------------------------+
| +NodeByLabelScan | 3 | 3 | 4 | p | :Node |
+-------------------------------+----------------+------+---------+----------------------+------------------------------------------------------------------------------------------+
Total database accesses: 19
注意，在前面介绍创建前缀的
WITH步骤时，我确实有点作弊，因为我注意到它改进了执行计划和数据库访问MATCH (p:Node), (c:Node)
USING INDEX c:Node(treeNumber)
WHERE c.treeNumber STARTS WITH p.treeNumber
AND p <> c
AND NOT substring(c.treeNumber, length(p.treeNumber) + 1) CONTAINS '.'
RETURN p, c
其执行计划如下：
Compiler CYPHER 3.0
Planner RULE
Runtime INTERPRETED
+--------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------+
| Operator | Rows | DB Hits | Variables | Other |
+--------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------+
| +Filter | 2 | 9 | c, p | NOT(p == c) AND NOT(Contains(SubstringFunction(c.treeNumber,Add(length(p.treeNumber),{ AUTOINT0}),None),{ AUTOSTRING1})) |
| | +------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------+
| +SchemaIndex | 6 | 12 | c -- p | PrefixSeekRangeExpression(p.treeNumber); :Node(treeNumber) |
| | +------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------+
| +NodeByLabel | 3 | 4 | p | :Node |
+--------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------+
Total database accesses: 25
最后，对于记录，我编写的原始查询（即没有提示）的执行计划是：
Compiler CYPHER 3.0
Planner COST
Runtime INTERPRETED
+--------------------+----------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Operator | Estimated Rows | Rows | DB Hits | Variables | Other |
+--------------------+----------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| +ProduceResults | 2 | 2 | 0 | c, p | p, c |
| | +----------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| +Filter | 2 | 2 | 21 | c, p | NOT(p == c) AND StartsWith(c.treeNumber,p.treeNumber) AND NOT(Contains(SubstringFunction(c.treeNumber,Add(length(p.treeNumber),{ AUTOINT0}),None),{ AUTOSTRING1})) |
| | +----------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| +CartesianProduct | 9 | 9 | 0 | p -- c | |
| |\ +----------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | +NodeByLabelScan | 3 | 9 | 12 | c | :Node |
| | +----------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| +NodeByLabelScan | 3 | 3 | 4 | p | :Node |
+--------------------+----------------+------+---------+-----------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
Total database accesses: 37
不是更糟的：没有提示但有预先计算的前缀的是！这就是为什么你应该经常测量。