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elasticsearch/docs/reference/query-languages/query-dsl/joining-queries.md
Craig Taverner 94cad286bc
Restructure query-languages docs files for clarity (#124797) 
In a few previous PR's we restructured the ES|QL docs to make it possible to generate them dynamically.

This PR just moves a few files around to make the query languages docs easier to work with, and a little more organized like the ES|QL docs.

A bit part of this was setting up redirects to the new locations, so other repo's could correctly link to the elasticsearch docs.
2025-03-17 17:58:58 +01:00

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https://www.elastic.co/guide/en/elasticsearch/reference/current/joining-queries.html

Joining queries [joining-queries]

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.

nested query
Documents may contain fields of type nested. These fields are used to index arrays of objects, where each object can be queried (with the nested query) as an independent document.
has_child and has_parent queries
A join field relationship can exist between documents within a single index. The has_child query returns parent documents whose child documents match the specified query, while the has_parent query returns child documents whose parent document matches the specified query.

Also see the terms-lookup mechanism in the terms query, which allows you to build a terms query from values contained in another document.

Notes [joining-queries-notes]

Allow expensive queries [_allow_expensive_queries_2]

Joining queries will not be executed if search.allow_expensive_queries is set to false.