I am having 2 nodes lets say of 2 type 'Student' and 'Class'
Student have {id, name}.
Class have {id, name}.
Student can have optional relationship with Class node as 'ATTENDS'.
(s:Student)-[r:ATTENDS]->(c:Class).
[r:ATTENDS] - Optional relationship. (present or may not present)
I want student record as it's all properties. If present relationship then class_name will match with present "Class" node else class_name will be null.
{student_id,student_name,class_name}
I tried by cypher query, but not getting result. Please help.
OPTIONAL MATCH (s:Student)-[:ATTENDS]->(c:Class) WHERE s.id =1
RETURN s.id AS student_id , s.name as student_name, c.name as class_name
By this query, if relationship exists then all values, if no relationship exists then all values are null.
If you don't care about the type of relation, you could run
MATCH (student:Student {id :1})
OPTIONAL MATCH (s)-->(class:Class)
RETURN student.id, student.name, class.name
and you'll have no need to set aliases.
Got solution to this problem by trying different queries.
MATCH (s:Student {id :1})
OPTIONAL MATCH (s)-[:ATTENDS]->(c:Class)
RETURN s.id AS student_id , s.name as student_name, c.name as class_name
Need to first match required criteria and then optional match. If anyone have simpler solution then please post.
Wrote a graph-gist for this at http://gist.neo4j.org/?11110772
The short answer is:
MATCH (s:Student) OPTIONAL MATCH (s)-->(c:Course)
RETURN s.name, c.name
Read the gist for more details. http://gist.neo4j.org/?11110772
Note that you cannot ignore the first MATCH. If the entire query is optional, nothing will be retrieved. In SQL you also have a non optional query on one table and then a left join to the second, optional, table.
Related
I have 3 Nodes:
:User which has a unique id property
:Palette which has a unique name property
:Color which has a unique hex property
When a user saves a pallete I would like to:
create a new pallete if a palette with this name does not exist, and add a :CREATED relationship from the :User to the :Palette
create a :SAVED relationship from the :User to the :Palette if one does not exist
Afterwards I would like to delete all :INCLUDES relationships that this :Palette has to :Color nodes inside the database (in order to create new ones afterwards).
This is my query (I replaced the variables with hardcoded strings so it's easier to execute):
MATCH (u:User)
WHERE u.id = '4f3d1904'
MERGE (p:Palette {name: 'Test'})
ON CREATE
SET p.name = "Test"
MERGE (u)-[cr:CREATED]->(p)
MERGE (u)-[sa:SAVED]->(p)
MATCH (p:Palette {name: 'Test'})-[in:INCLUDES]->()
DELETE in
When running the query I get the following error:
WITH is required between MERGE and MATCH (line 8, column 1 (offset: 181))
"MATCH (p:Palette {name: 'Test'})-[in:INCLUDES]->()"
^
But if I add a WITH I get the following:
MATCH (u:User)
WHERE u.id = '4f3d1904'
MERGE (p:Palette {name: 'Test'})
ON CREATE
SET p.name = "Test"
MERGE (u)-[cr:CREATED]->(p)
MERGE (u)-[sa:SAVED]->(p)
WITH
MATCH (p:Palette {name: 'Test'})-[in:INCLUDES]->()
DELETE in
Invalid input ')': expected whitespace or a relationship pattern (line 9, column 32 (offset: 217))
"MATCH (p:Palette {name: 'Test'})-[in:INCLUDES]->()"
^
What am I doing wrong?
MERGE and MATCH stages (or MATCH and MATCH) require a WITH between them in order to use the result of the former in the latter.
In your case you can use the p that you already have like this:
...
WITH p
MATCH (p)-[in:INCLUDES]->()
DELETE in
So you won't need to find it again. without the WITH, it is like two different queries.
I am new to Neo4j and have a query that I want to improve. Any help or recommendations would be appreciated.
MATCH (s:Source),
(s)-[:SourceContext]->(c:Context),
(c)-[:ContextFunction]->(f:Function)
OPTIONAL MATCH (c)<-[*1..2]-(e:Entity)
OPTIONAL MATCH (c)<-[*1..2]-(au:Author)
OPTIONAL MATCH (c)<-[*1..2]-(p:Period)
OPTIONAL MATCH (c)<-[*1..2]-(u:Unit)
OPTIONAL MATCH (c)<-[*1..2]-(a:AttributeSet)
OPTIONAL MATCH (c)<-[*1..2]-(t:Timeseries)
WITH e,t,p,u,s,a,f,au
WHERE
(t.id in [3450] or t.id is null) AND
(e.id in [16260] or e.id is null)
AND s.id = 16
AND (a.id = 0 or a.id is NULL)
return {SourceID: s.id, EntityID: e.id, TimeSeriesID: t.id, PeriodID: p.id, UnitID: u.id, FunctionID: f.id, AttributeSetID: a.id}
See neo4j profile plan
here
Instead of traversing the whole graph, you will want to move the filtering part of the cypher queries sooner in the query.
MATCH (s:Source),
(s)-[:SourceContext]->(c:Context),
(c)-[:ContextFunction]->(f:Function)
WHERE s.id = 16
OPTIONAL MATCH (c)<-[*1..2]-(e:Entity)
WHERE e.id = 16260 or e.id is null
OPTIONAL MATCH (c)<-[*1..2]-(au:Author)
OPTIONAL MATCH (c)<-[*1..2]-(p:Period)
OPTIONAL MATCH (c)<-[*1..2]-(u:Unit)
OPTIONAL MATCH (c)<-[*1..2]-(a:AttributeSet)
WHERE a.id = 0 or a.id is NULL
OPTIONAL MATCH (c)<-[*1..2]-(t:Timeseries)
WHERE t.id = 3450 or t.id is null
WITH e,t,p,u,s,a,f,au
return {SourceID: s.id, EntityID: e.id, TimeSeriesID: t.id, PeriodID: p.id, UnitID: u.id, FunctionID: f.id, AttributeSetID: a.id}
This should greatly improve the query performance as you will be starting from only a single Source node instead of traversing all the source nodes in your graph.
It would also help if your graph model supports adding relationship types to the OPTIONAL MATCHes.
For example:
OPTIONAL MATCH (c)<-[:HAS_AUTHOR*1..2]-(au:Author)
This way you avoid traversing all the relationship types in each OPTIONAL MATCH.
If not, there are still some improvements you could make.
You could run the
OPTIONAL MATCH (c)<-[*1..2]-(node)
And then filter the results based on node type:
CASE WHEN node:Author THEN ... ELSE ... END
I need a MATCH where either relationship is true. I understand the (person1)-[:r1|:r2]-(person2). The problem I am having is that one of the MATCH traverse through another node. IE:
(p1:person)-[:FRIEND]-(p2:person)-[:FRIEND]-(p3:person)
So I want this kind of logic. The enemy of my enemy is my friend. And my friend is my friend. Output list of all the names who are my friend. I also limit the relationship to a particular value.
Something like:
MATCH (p1:Person)-[:ENEMY{type:'human'}]-(myEnemy:Person)-[enemy2:ENEMY{type:'human'}]-(myFriend:Person)
OR (p1:Person)-[friend:FRIEND{type:'human'}]-(myFriend:Person)
RETURN p1.name, myFriend.name
I need one list that I can then do aggregation on.
This is my first posting....so if my question is a mess...hit me with your feedback and I will clarify :)
You can use the UNION clause to combine 2 queries and also remove duplicate results:
MATCH (p:Person)-[:ENEMY{type:'human'}]-(:Person)-[:ENEMY{type:'human'}]-(f:Person)
WHERE ID(p) < ID(f)
RETURN p.name AS pName, f.name AS fName
UNION
MATCH (p:Person)-[:FRIEND{type:'human'}]-(f:Person)
WHERE ID(p) < ID(f)
RETURN p.name AS pName, f.name AS fName
The ID(p) < ID(f) filtering is done to avoid having the same pair of Person names being returned twice (in reverse order).
[UPDATE]
To get a count of how many friends each Person has, you can take advantage of the new CALL subquery syntax (in neo4j 4.0) to do post-union processing:
CALL {
MATCH (p:Person)-[:ENEMY{type:'human'}]-(:Person)-[:ENEMY{type:'human'}]-(f:Person)
WHERE ID(p) < ID(f)
RETURN p.name AS pName, f
UNION
MATCH (p:Person)-[:FRIEND{type:'human'}]-(f:Person)
WHERE ID(p) < ID(f)
RETURN p.name AS pName, f
}
RETURN pName, COUNT(f) AS friendCount
I have a following Neo4j Cypher query that checks if relationship exists between User and entity and returns boolean result:
MATCH (u:User) WHERE u.id = {userId} MATCH (entity) WHERE id(entity) = {entityGraphId} RETURN EXISTS( (u)<-[:OWNED_BY]-(entity) )
Please help to rewrite this query in order to be able to accept a collection of {entityGraphIds} instead of a single {entityGraphId} and check if a relationship exists between User and any entities with these {entityGraphIds}.
For example, I have user1 and entity1, entity2. user1 has a relationship with entity2. I'll pass {user.id} like {userId} and {entity1.id, entity2.id} like {entityGraphIds} and this query should return true.
I believe you can simply use the IN operator. Considering these parameters:
:params {userId: 1, entityGraphIds : [2,3,4]}
Then, the query:
MATCH (u:User) WHERE u.id = {userId}
MATCH (entity) WHERE id(entity) IN ({entityGraphIds})
RETURN EXISTS( (u)<-[:OWNED_BY]-(entity) )
EDIT:
If you are trying to return true when :User is connected to at least 1 entity, then you can simplify your query to:
OPTIONAL MATCH (u:User)<-[:OWNED_BY]-(entity:Entity)
WHERE u.id = {userId} AND id(entity) IN ({entityGraphIds})
RETURN u IS NOT NULL
How can I do an match in clause in cypher
e.g. I'd like to find movies with ids 1, 2, or 3.
match (m:movie {movie_id:("1","2","3")}) return m
if you were going against an auto index the syntax was
START n=node:node_auto_index('movie_id:("123", "456", "789")')
how is this different against a match clause
The idea is that you can do:
MATCH (m:movie)
WHERE m.movie_id in ["1", "2", "3"]
However, this will not use the index as of 2.0.1. This is a missing feature in the new label indexes that I hope will be resolved soon. https://github.com/neo4j/neo4j/issues/861
I've found a (somewhat ugly) temporary workaround for this.
The following query doesn't make use of an index on Person(name):
match (p:Person)... where p.name in ['JOHN', 'BOB'] return ...;
So one option is to repeat the entire query n times:
match (p:Person)... where p.name = 'JOHN' return ...
union
match (p:Person)... where p.name = 'BOB' return ...
If this is undesirable then another option is to repeat just a small query for the id n times:
match (p:Person) where p.name ='JOHN' return id(p)
union
match (p:Person) where p.name ='BOB' return id(p);
and then perform a second query using the results of the first:
match (p:Person)... where id(p) in [8,16,75,7] return ...;
Is there a way to combine these into a single query? Can a union be nested inside another query?