elasticsearch/docs/reference/esql/functions/kibana/docs/bucket.md

BUCKET

Creates groups of values - buckets - out of a datetime or numeric input. The size of the buckets can either be provided directly, or chosen based on a recommended count and values range.

FROM employees
| WHERE hire_date >= "1985-01-01T00:00:00Z" AND hire_date < "1986-01-01T00:00:00Z"
| STATS hire_date = MV_SORT(VALUES(hire_date)) BY month = BUCKET(hire_date, 20, "1985-01-01T00:00:00Z", "1986-01-01T00:00:00Z")