neo4j cypher Match command concatenation

Question

are these two Chypher statements identical:

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

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

Answer 1

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.

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

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

2. 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 |                |
   ==> +----------------+---------------+------+--------+----------------+----------------+