Achieving longestPath Using Cypher

While Cypher is optimized for finding the shortest path between two nodes, with such functionality as shortestPath(), it does not have the same sort of function for longest path. In some cases, you may want this, and not the shortest… Read more →

Resetting query cardinality

As queries execute, they build up result rows. Cypher executes operations per-row. When a query is made up of completely separate parts, unrelated to each other, and you don’t want to split the single query into multiple queries, you sometimes… Read more →

Large Delete Transaction Best Practices in Neo4j

In order to achieve the best performance, and avoid negative effects on the rest of the system, consider these best practices when processing large deletes. Start by identifying which situation you are in: Deleting the entire graph database, so you… Read more →

How to write a Cypher query to return the top N results per category

The following Cypher describes how you can display the Top 5 test scores within an entire :Score population broken out by a field_of_study property. create (n:Score {student_id: ‘DC001’, score: 89, field_of_study: ‘chemistry’}); create (n:Score {student_id: ‘MK812’, score: 97, field_of_study: ‘chemistry’});… Read more →

Alternatives to UNION queries

While UNIONs can be useful for certain cases, they can often be avoided completely with small changes to the query. In this article we’ll present various example cases where a UNION isn’t necessary, and a simple Cypher query will do.… Read more →

A note on OPTIONAL MATCHes

An OPTIONAL MATCH matches patterns against your graph database, just like a MATCH does. The difference is that if no matches are found, OPTIONAL MATCH will use a null for missing parts of the pattern. OPTIONAL MATCH could be considered… Read more →

Understanding transaction and lock timeouts

One way to handle runaway queries is to impose a time limit that will terminate a query when exceeded. There are some subtleties here that need to be understood to ensure proper behavior and avoid confusion. Defining a transaction timeout… Read more →

Neo4j & JDBC: the Neo4j JDBC Driver vs. BI Connector

This page describes the connection between JDBC and Neo4j, and when users should use the BI Connector, vs. when they should use the Neo4j JDBC Driver. To begin with, let’s start that JDBC is a transport; that is, it is… Read more →

Post-UNION processing

Cypher does not allow further processing of UNION or UNION ALL results, since RETURN is required in all queries of the union. Here are some workarounds. Post-UNION processing in Neo4j 4.0 With Neo4j 4.0, post-UNION processing is now possible via… Read more →

Understanding how MERGE works

What is MERGE, and how does it work? The MERGE clause ensures that a pattern exists in the graph. Either the pattern already exists, or it needs to be created. In this way, it’s helpful to think of MERGE as… Read more →

Why doesn’t my WHERE clause work?

It can be frustrating when it seems like a WHERE clause isn’t working. You can use these approaches to figure out what’s wrong. Check for WHERE clauses following OPTIONAL MATCH WHERE clauses can’t be used on their own, they are… Read more →

How to check for time range overlap in Cypher

Neo4j 3.4 introduced temporal types into Cypher, so now we have dates, dateTimes, and their local versions, too, as well as durations. While we don’t have a type for time ranges, we can use two temporal instants as the start… Read more →

All shortest paths between a set of nodes

Consider a number of arbitrary nodes, A,B,C,D,E,F,…​.. I wish to return all of the shortest paths between these nodes. The nodes may have many edges between them, but anticipate a maximum of 4. The graph is complex and non hierarchical… Read more →

How do I display the nodes with the most properties

To display the nodes with the most properties defined, run the following Cypher: MATCH (n) RETURN labels(n), keys(n), size(keys(n)), count(*) ORDER BY size(keys(n)) DESC Representative output is similar to: labels(n) keys(n) size(keys(n)) count(*) [Movie] [TotalRevenue, year_of_release, name, id] 4 1… Read more →

Using Cypher to generate Cypher statements to recreate indexes and constraints

The following can be used to extract index defintions and constraint defintions from an existing database and the resultant output can be played back on another Neo4j database. For example with the :play movies dataset as when run from the… Read more →

How to avoid using excessive memory on deletes involving dense nodes

In situations where you know you need to delete a bunch of nodes (and by rule their relationships as well), it can be tempting to simply use DETACH DELETE and be done with it. However, this can become problematic if… Read more →

How do I produce an inventory of statistics on nodes, relationships, properties

MATCH (n) WHERE rand() <= 0.1 WITH labels(n) as labels, size(keys(n)) as props, size((n)–()) as degree RETURN DISTINCT labels, count(*) AS NumofNodes, avg(props) AS AvgNumOfPropPerNode, min(props) AS MinNumPropPerNode, max(props) AS MaxNumPropPerNode, avg(degree) AS AvgNumOfRelationships, min(degree) AS MinNumOfRelationships, max(degree) AS MaxNumOfRelationships… Read more →

Conditional Cypher Execution

At some point you’re going to write a Cypher query requiring some conditional logic, where you want different Cypher statements executed depending on the case. At this point in time Cypher does not include native conditional functionality to address this… Read more →

How to generate sysinfo output from Cypher

If you need to generate the equivalent output from command :sysinfo as run from the Neo4j Browser at http://localhost:7474 this can be achieved by running the following Cypher call dbms.queryJmx(“org.neo4j:instance=kernel#0,name=Store file sizes”) yield attributes with keys(attributes) as k , attributes… Read more →