/**
 * Aggregation helpers — return AggregationSpec objects used in metric definitions.
 *
 * @example
 * ```ts
 * import { sum, count, countDistinct, avg } from '@hypequery/serve';
 *
 * const totalRevenue = Orders.metric("totalRevenue", {
 *   value: sum("amount"),
 * });
 *
 * const orderCount = Orders.metric("orderCount", {
 *   value: count("id"),
 * });
 * ```
 */
import type { AggregationSpec } from './types.js';
export declare function sum(field: string): AggregationSpec;
export declare function count(field: string): AggregationSpec;
export declare function countDistinct(field: string): AggregationSpec;
export declare function avg(field: string): AggregationSpec;
export declare function min(field: string): AggregationSpec;
export declare function max(field: string): AggregationSpec;
/** Approximate percentile of a numeric field at `level` in [0, 1]. */
export declare function percentile(field: string, level: number): AggregationSpec;
/** Median — sugar for `percentile(field, 0.5)`. */
export declare function median(field: string): AggregationSpec;
/** Value of `field` on the row where `by` is greatest. */
export declare function argMax(field: string, by: string): AggregationSpec;
/** Value of `field` on the row where `by` is smallest. */
export declare function argMin(field: string, by: string): AggregationSpec;
/** Sample standard deviation. */
export declare function stddev(field: string): AggregationSpec;
/** Sample variance. */
export declare function variance(field: string): AggregationSpec;
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