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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