Chapter 25. High-Level Concepts
Like the query DSL, aggregations have a composable syntax: independent units of functionality can be mixed and matched to provide the custom behavior that you need. This means that there are only a few basic concepts to learn, but nearly limitless combinations of those basic components.
To master aggregations, you need to understand only two main concepts:
- Buckets
-
Collections of documents that meet a criterion
- Metrics
-
Statistics calculated on the documents in a bucket
That’s it! Every aggregation is simply a combination of one or more buckets and zero or more metrics. To translate into rough SQL terms:
SELECT
COUNT
(
color
)
FROM
table
GROUP
BY
color
Buckets are conceptually similar to grouping in SQL, while metrics are similar
to COUNT()
, SUM()
, MAX()
, and so forth.
Let’s dig into both of these concepts and see what they entail.
Buckets
A bucket is simply a collection of documents that meet a certain criteria:
-
An employee would land in either the male or female ...
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