Performing full SQL-style joins in a distributed system like Elasticsearch is prohibitively expensive. Instead, Elasticsearch offers two forms of join which are designed to scale horizontally.
Documents may contains fields of type
nested. These fields are used to index arrays of objects, where each object can be queried (with the
nestedquery) as an independent document.
A parent-child relationship can exist between two
document types within a single index. The
has_childquery returns parent documents whose child documents match the specified query, while the
has_parentquery returns child documents whose parent document matches the specified query.
See Nested Query
See Has Child Query