import type { FieldReference } from '../query-items/field-references';
import type { ExprValue } from '../types/expr-value';
import type { FieldSpace } from '../types/field-space';
import { ExprAggregateFunction } from './expr-aggregate-function';
export declare class ExprCount extends ExprAggregateFunction {
    readonly source?: FieldReference | undefined;
    elementType: string;
    constructor(source?: FieldReference | undefined);
    defaultFieldName(): string | undefined;
    returns(ev: ExprValue): ExprValue;
    getExpression(_fs: FieldSpace): ExprValue;
}