neo4j cypher匹配命令连接

Question

这两个Chypher声明是否相同:

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

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

Answer 1

2 Cypher声明不完全相同.我们可以使用PROFILE命令来显示这一点,该命令向您展示了Cypher引擎如何执行查询.

在以下示例中,查询都以此结束RETURN a, c,因为您不能拥有bare MATCH子句.

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

1. 第一个查询

   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. 第二个查询

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