Database Reference
In-Depth Information
6.4. Advanced Cypher
You've learned how to write and execute fairly complex Cypher queries so far, but there's
muchmoretoCypherthanthat.Inthissectionwe'regoingtotakealookatsomeofthead-
vanced features in Cypher, like data aggregation, Cypher functions, and chaining multiple
queries together. Let's start with data aggregation.
6.4.1. Aggregation
Just like
GROUP BY
in SQL, Cypher supports aggregating functions in queries. Instead of
using a dedicated
GROUP BY
clause, the grouping key in Cypher is defined as all non-ag-
gregating results of the query. Here's how you could count the number of friends for each
user in the graph:
You're looking at the entire graph in this example, so all nodes are used as starting nodes
. For each
user
node, you match their direct friends by following one level of the
IS_FRIEND_OF
relationship
. The
return
clause contains one non-aggregating
entry (
user
node) and one aggregated function (
count
) . This means that you're us-
ing the
user
node to group the counts by, getting one result row per user. You can use the
aggregated values to order the entire result set in the
order by
clause as well
.
In addition to the
count
function, Cypher supports all the usual aggregation functions
from SQL:
SUM
for summing numeric values,
AVG
for calculating averages, and
MAX
and
MIN
for finding the maximum or minimum values of numeric properties.
To find the average age of all John's friends, you can use the following query:
