neo4j cypher 匹配命令串联

Question

这两个 Chypher 语句是否相同:

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

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

Answer 1

2 个 Cypher 语句并不相同。我们可以使用 PROFILE command 来显示这一点，它向您展示了 Cypher 引擎将如何执行查询。

在下面的示例中，查询都以 RETURN a, c 结尾，因为您不能有一个裸露的 MATCH 子句。

如您所见，第一个查询有一个 NOT(r == r2) 过滤器，而第二个查询没有。这是因为 Cypher 确保单个 MATCH 子句的结果不包含重复关系。

1. 第一次查询

   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 |                |
   ==> +----------------+---------------+------+--------+----------------+----------------+
   ==> 
   

2. 第二次查询

   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 |                |
   ==> +----------------+---------------+------+--------+----------------+----------------+