equi_height.h File Reference

Equi-height histogram. More...

#include <cstddef>
#include <string>
#include "sql/histograms/equi_height_bucket.h"
#include "sql/histograms/histogram.h"
#include "sql/histograms/value_map_type.h"
#include "sql/mem_root_array.h"

Go to the source code of this file.

Classes
class	histograms::Equi_height< T >

Namespaces
namespace	histograms
namespace	histograms::equi_height

Detailed Description

Equi-height histogram.

This file defines the class representing an equi-height histogram.

An equi-height histogram converted to a JSON object, follows the following "schema":

{ Last time the histogram was updated. As of now, this means "when the histogram was created" (incremental updates are not supported). Date/time is given in UTC. – J_DATETIME "last-updated": "2015-11-04 15:19:51.000000",

Histogram type. Always "equi-height" for equi-height histograms. – J_STRING "histogram-type": "equi-height",

Fraction of NULL values. This is the total fraction of NULL values in the original data set. – J_DOUBLE "null-values": 0.1,

Histogram buckets. May be an empty array, if for instance the source only contain NULL values. – J_ARRAY "buckets": [ [ Lower inclusive value. – Data type depends on the source column. "0",

Upper inclusive value. – Data type depends on the source column. "002a38227ecc7f0d952e85ffe37832d3f58910da",

Cumulative frequence – J_DOUBLE 0.001978728666831561,

Number of distinct values in this bucket. – J_UINT 10 ] ] }