aggregation
Grouping rows and computing a value over each group. In Cypher the grouping keys are whatever expressions in the same clause are not aggregated.
Example
One row per person, counting the films each acted in.
cypher
MATCH (p:Person)-[:ACTED_IN]->(m:Movie)
RETURN p.name, count(m) AS filmscount(m) is the aggregate. p.name is the only other expression in the clause, so it is the grouping key. Adding m.year beside it would group by person and year instead, and return a row for each.
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