Implementation:Apache Druid MeasurePattern

Knowledge Sources	Apache_Druid
Domains	Web_Console, Explore_View
Last Updated	2026-02-10 10:00 GMT

Overview

An immutable value class representing a simplified aggregate measure pattern (count, sum, min, max, or countDistinct) over a column.

Description

The MeasurePattern class models common aggregate patterns found in Druid queries. It can be constructed directly from aggregate type and column name, fitted from an existing SqlExpression via the static `fit` method, or created from a Column object via `fromColumn`. The class supports conversion to and from SqlExpression AST nodes (e.g., COUNT(*), SUM("col"), COUNT(DISTINCT "col")), pretty-printing for display, and immutable changes to the aggregate type or column. The supported aggregate types are: count, sum, min, max, and countDistinct.

Usage

Used in the explore view's measure configuration UI to represent, edit, and convert between user-facing measure patterns and their corresponding SQL aggregate expressions.

Code Reference

Source Location

• Repository: Apache Druid
• File: web-console/src/views/explore-view/models/measure-pattern.ts
• Lines: 1-148

Signature

export type MeasurePatternAggregate = 'count' | 'sum' | 'min' | 'max' | 'countDistinct';

export class MeasurePattern {
  static AGGREGATES: MeasurePatternAggregate[];
  static fromColumn(column: Column): MeasurePattern;
  static fit(expression: SqlExpression): MeasurePattern | undefined;

  public readonly aggregate: MeasurePatternAggregate;
  public readonly column: string;

  constructor(value: MeasurePatternValue);
  valueOf(): MeasurePatternValue;
  toString(): string;
  prettyPrint(): string;
  changeAggregate(aggregate: MeasurePatternAggregate): MeasurePattern;
  changeColumn(column: string): MeasurePattern;
  toExpression(): SqlExpression;
}

Import

import { MeasurePattern } from '../models/measure-pattern';

I/O Contract

Inputs

Name	Type	Required	Description
value	MeasurePatternValue	Yes	Object with aggregate type and optional column name (defaults to '*')
expression	SqlExpression	Yes	A SQL aggregate expression to reverse-engineer into a MeasurePattern (fit)
column	Column	Yes	A druid-query-toolkit Column to derive a default measure pattern from (fromColumn)

Outputs

Name	Type	Description
(return)	MeasurePattern	A new or modified MeasurePattern instance
(return)	SqlExpression	The SQL aggregate expression corresponding to this pattern (toExpression)
(return)	string	A human-readable description like "Count", "Sum revenue", "Dist. user_id" (prettyPrint)

Usage Examples

Create from a column and convert to expression

import { MeasurePattern } from '../models/measure-pattern';

const pattern = MeasurePattern.fromColumn({ name: 'revenue', sqlType: 'DOUBLE', nativeType: 'DOUBLE' });
const expr = pattern.toExpression();
// expr represents: SUM("revenue")

Fit a pattern from an existing SQL expression

import { MeasurePattern } from '../models/measure-pattern';
import { SqlFunction } from 'druid-query-toolkit';

const pattern = MeasurePattern.fit(SqlFunction.COUNT_STAR);
// pattern.aggregate === 'count'
// pattern.column === '*'

Change aggregate type

const sumPattern = new MeasurePattern({ aggregate: 'sum', column: 'revenue' });
const maxPattern = sumPattern.changeAggregate('max');
// maxPattern.toExpression() represents: MAX("revenue")

Related Pages

• Environment:Apache_Druid_Web_Console_Development