Create on NOT MATCH command for Neo4j's CQL? - neo4j

Question

I have a non-unique node (:Neighborhood) that uniquely appears [:IN] a (:City) node. I would like to create a new neighborhood node and establish its relationship ONLY if that neighborhood node does not exist in that city. There can be multiple neighborhoods that have the same name, but each neighborhood must appear uniquely appear in the property city.
Following the advice from the Gil's answer here: Return node if relationship is not present, how can I do something like:
MATCH a WHERE NOT (a:Neighborhood {name : line.Neighborhood})-[r:IN]->(c:City {name : line.City})
ON MATCH SET (a)-[r]-(c)
So then it would only create a new neighborhood node if it doesn't already exist in the city.
**UPDATE:**I upgraded and profiled it and still can't take advantage of any optimizations...
PROFILE LOAD CSV WITH HEADERS FROM "file://THEFILE" as line
WITH line LIMIT 0
MATCH (c:City { name : line.City})
MERGE (n:Neighborhood {name : toInt(line.Neighborhood)})-[:IN]->(c)
;
+--------------+------+--------+---------------------------+------------------------------+
| Operator | Rows | DbHits | Identifiers | Other |
+--------------+------+--------+---------------------------+------------------------------+
| EmptyResult | 0 | 0 | | |
| UpdateGraph | 5 | 16 | anon[340], b, neighborhood, line | MergePattern |
| SchemaIndex | 5 | 10 | b, line | line.City; :City(name) |
| ColumnFilter | 5 | 0 | line | keep columns line |
| Filter | 5 | 0 | anon[216], line | anon[216] |
| Extract | 5 | 0 | anon[216], line | anon[216] |
| Slice | 5 | 0 | line | { AUTOINT0} |
| LoadCSV | 5 | 0 | line | |
+--------------+------+--------+---------------------------+------------------------------+

Answer 1

I think you could simply use MERGE for this:
MATCH (c:City {name: line.City})
MERGE c<-[:IN]-(a:Neighborhood {name : line.Neighborhood})
If you haven't already imported all of the cities, you can create those with MERGE:
MATCH (c:City {name: line.City})
MERGE c<-[:IN]-(a:Neighborhood {name : line.Neighborhood})
But beware of the Eager operator:
http://www.markhneedham.com/blog/2014/10/23/neo4j-cypher-avoiding-the-eager/
In short: You should run your LOAD CSV (I assume that's what you're doing here) twice, once to load the cities and once to load the neighborhoods.