neo4j cypher匹配命令串联 [英] neo4j cypher Match command concatenation

问题描述

这两个Chypher语句是否相同:

are these two Chypher statements identical:

//first
match (a)-[r]->(b),b-[r2]->c

//second
match (a)-[r]->(b)
match b-[r2]->c

推荐答案

2个Cypher语句不同.我们可以使用 PROFILE命令来显示此信息您将了解Cypher引擎如何执行查询.

The 2 Cypher statements are NOT identical. We can show this by using the PROFILE command, which shows you how the Cypher engine would perform a query.

在以下示例中，所有查询均以RETURN a, c结尾，因为您不能有裸露的MATCH子句.

In the following examples, the queries all end with RETURN a, c, since you cannot have a bare MATCH clause.

如您所见，第一个查询具有一个NOT(r == r2)过滤器，而第二个查询则没有.这是因为Cypher确保单个MATCH子句的结果不包含重复的关系.

As you can see, the first query has a NOT(r == r2) filter that the second query does not. This is because Cypher makes sure that the result of a single MATCH clause does not contain duplicate relationships.

1. 第一个查询

1. First query

profile match (a)-[r]->(b),b-[r2]->c return a,c;
==> +-----------------------------------------------+
==> | a                     | c                     |
==> +-----------------------------------------------+
==> | Node[1]{name:"World"} | Node[0]{name:"World"} |
==> +-----------------------------------------------+
==> 1 row
==> 2 ms
==> 
==> Compiler CYPHER 2.3
==> 
==> Planner COST
==> 
==> Runtime INTERPRETED
==> 
==> Projection
==>   |
==>   +Filter
==>     |
==>     +Expand(All)(0)
==>       |
==>       +Expand(All)(1)
==>         |
==>         +AllNodesScan
==> 
==> +----------------+---------------+------+--------+----------------+----------------+
==> |       Operator | EstimatedRows | Rows | DbHits |    Identifiers |          Other |
==> +----------------+---------------+------+--------+----------------+----------------+
==> |     Projection |             1 |    1 |      0 | a, b, c, r, r2 |           a; c |
==> |         Filter |             1 |    1 |      0 | a, b, c, r, r2 |   NOT(r == r2) |
==> | Expand(All)(0) |             1 |    2 |      4 | a, b, c, r, r2 | (b)-[r2:]->(c) |
==> | Expand(All)(1) |             2 |    2 |      8 |        a, b, r |  (b)<-[r:]-(a) |
==> |   AllNodesScan |             6 |    6 |      7 |              b |                |
==> +----------------+---------------+------+--------+----------------+----------------+
==> 

第二个查询

Second query

profile match (a)-[r]->(b) match b-[r2]->c return a,c;
==> +-----------------------------------------------+
==> | a                     | c                     |
==> +-----------------------------------------------+
==> | Node[1]{name:"World"} | Node[1]{name:"World"} |
==> | Node[1]{name:"World"} | Node[0]{name:"World"} |
==> +-----------------------------------------------+
==> 2 rows
==> 2 ms
==> 
==> Compiler CYPHER 2.3
==> 
==> Planner COST
==> 
==> Runtime INTERPRETED
==> 
==> Projection
==>   |
==>   +Expand(All)(0)
==>     |
==>     +Expand(All)(1)
==>       |
==>       +AllNodesScan
==> 
==> +----------------+---------------+------+--------+----------------+----------------+
==> |       Operator | EstimatedRows | Rows | DbHits |    Identifiers |          Other |
==> +----------------+---------------+------+--------+----------------+----------------+
==> |     Projection |             1 |    2 |      0 | a, b, c, r, r2 |           a; c |
==> | Expand(All)(0) |             1 |    2 |      4 | a, b, c, r, r2 | (b)-[r2:]->(c) |
==> | Expand(All)(1) |             2 |    2 |      8 |        a, b, r |  (b)<-[r:]-(a) |
==> |   AllNodesScan |             6 |    6 |      7 |              b |                |
==> +----------------+---------------+------+--------+----------------+----------------+

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