79 lines
2.5 KiB
Plaintext
79 lines
2.5 KiB
Plaintext
[role="xpack"]
|
|
[testenv="basic"]
|
|
[[sql-functions-grouping]]
|
|
=== Grouping Functions
|
|
|
|
beta[]
|
|
|
|
Functions for creating special __grouping__s (also known as _bucketing_); as such these need to be used
|
|
as part of the <<sql-syntax-group-by, grouping>>.
|
|
|
|
[[sql-functions-grouping-histogram]]
|
|
==== `HISTOGRAM`
|
|
|
|
.Synopsis:
|
|
[source, sql]
|
|
----
|
|
HISTOGRAM(numeric_exp<1>, numeric_interval<2>)
|
|
HISTOGRAM(date_exp<3>, date_time_interval<4>)
|
|
----
|
|
|
|
*Input*:
|
|
|
|
<1> numeric expression (typically a field)
|
|
<2> numeric interval
|
|
<3> date/time expression (typically a field)
|
|
<4> date/time <<sql-functions-datetime-interval, interval>>
|
|
|
|
*Output*: non-empty buckets or groups of the given expression divided according to the given interval
|
|
|
|
.Description
|
|
|
|
The histogram function takes all matching values and divides them into buckets with fixed size matching the given interval, using (roughly) the following formula:
|
|
|
|
[source, sql]
|
|
----
|
|
bucket_key = Math.floor(value / interval) * interval
|
|
----
|
|
|
|
NOTE:: The histogram in SQL does *NOT* return empty buckets for missing intervals as the traditional <<search-aggregations-bucket-histogram-aggregation, histogram>> and <<search-aggregations-bucket-datehistogram-aggregation, date histogram>>. Such behavior does not fit conceptually in SQL which treats all missing values as `NULL`; as such the histogram places all missing values in the `NULL` group.
|
|
|
|
`Histogram` can be applied on either numeric fields:
|
|
|
|
|
|
["source","sql",subs="attributes,callouts,macros"]
|
|
----
|
|
include-tagged::{sql-specs}/docs.csv-spec[histogramNumeric]
|
|
----
|
|
|
|
or date/time fields:
|
|
|
|
["source","sql",subs="attributes,callouts,macros"]
|
|
----
|
|
include-tagged::{sql-specs}/docs.csv-spec[histogramDate]
|
|
----
|
|
|
|
Expressions inside the histogram are also supported as long as the
|
|
return type is numeric:
|
|
|
|
["source","sql",subs="attributes,callouts,macros"]
|
|
----
|
|
include-tagged::{sql-specs}/docs.csv-spec[histogramNumericExpression]
|
|
----
|
|
|
|
Do note that histograms (and grouping functions in general) allow custom expressions but cannot have any functions applied to them in the `GROUP BY`. In other words, the following statement is *NOT* allowed:
|
|
|
|
["source","sql",subs="attributes,callouts,macros"]
|
|
----
|
|
include-tagged::{sql-specs}/docs.csv-spec[expressionOnHistogramNotAllowed]
|
|
----
|
|
|
|
as it requires two groupings (one for histogram followed by a second for applying the function on top of the histogram groups).
|
|
|
|
Instead one can rewrite the query to move the expression on the histogram _inside_ of it:
|
|
|
|
["source","sql",subs="attributes,callouts,macros"]
|
|
----
|
|
include-tagged::{sql-specs}/docs.csv-spec[histogramDateExpression]
|
|
----
|