Multiple Match statements in Neo4j - neo4j

Question

I have a list of MATCH statements which are totally unrelated to each other. But if I execute them like
MATCH (a:Person),(b:InProceedings) WHERE a.identifier = 'person/joseph-valeri' and b.identifier = 'conference/edm2008/paper/209' CREATE (a)-[r:creator]->(b)
MATCH (a:Person),(b:InProceedings) WHERE a.identifier = 'person/nell-duke' and b.identifier = 'conference/edm2008/paper/209' CREATE (a)-[r:creator]->(b)
But if I execute them at once I get the following error:
WITH is required between CREATE and MATCH (line 2, column 1)
What changes should I incorporate?
(I am new to Neo4j)

Answer 1

Does this need to happen in a single transaction? In which case you should be matching your nodes up front before performing the create:
MATCH (jo:Person{identifier:'person/joseph-valeri'}), (nell:Person{identifier:'person/nell-duke'}), (b:InProceedings{identifier:'conference/edm2008/paper/209'})
CREATE (jo)-[:creator]->(b), (nell)-[:creator]->(b)
If it's just the two creators you could change the create to:
CREATE (jo)-[:creator]->(b)<-[:creator]-(nell)
If this isn't what you want to achieve then effectively what you have posted is two distinct Cypher statements that you are trying to run as one, and the parser is getting confused.
Post comment edit
Given that you said millions I think that you are going to find the transaction time on performing the import prohibitive and therefore you should investigate the CSV import syntax (and specifically pay attention to PERIODIC COMMIT) if you can write to CSV instead of to the big Cypher dump?
If for some reason that is not an option and you are starting from empty then build slowly - creating nodes first. These are going to need names to keep the speed up (but these names aren't persisted, just constant in your Cypher query):
CREATE (a:Person{identifier:'person/joseph-valeri'}),
(b:Person{identifier:'person/nell-duke'}),
(zzz:Person{identifier:'person/do-you-really-want-person-in-all-these-identifiers'}),
(inProca:InProceedings{identifier:'conference/edm2008/paper/209'}),
(inProcb:InProceedings{identifier:'conference/edm2009/paper/209'})
You will have kept track of a, b .. zzz in your Python script allowing you to build the CREATE statment up with:
(a)-[:creator]->(inProcA), (zzz)-[:creator]-(inProcB)
Now if all of your nodes already exist and you just want to build the relationships in now, then you have the choice of:
Performing individual MATCH and CREATEs for each new relationship, exceuting them each individually. This looks like what your original code was doing. You should move the conditions into the MATCH rather than the WHERE clause.
MATCHing a large set of nodes and CREATEing new realtionships. This is more akin to what my initial code was doing and will require your script to be smart in generating the queries.
MERGEing existing nodes into new relationships.
Whatever you do, you'e going to need to batch the writes within the transaction or you're going to run out of memory - you can advise Neo4J to do this by using the USING PERIODIC COMMIT 50000 syntax, here is a great blog post on it.