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/*******************************************************************
 * © 2023 SAP SE or an SAP affiliate company. All rights reserved. *
 *******************************************************************/
package com.sap.cds.ql.cqn.transformation;

import java.util.List;

import com.google.common.annotations.Beta;
import com.sap.cds.ql.cqn.CqnElementRef;

/**
 * Transformation that groups the result set according to specified dimensions
 * and applies given transformations to each group.
 * 
 * The result set is the grouped input set after applying the transformations.
 * 
 * Two scenarios are common:
 * 
 * 1. the list of transformations is empty -> the output set contains the
 * distinct values of the dimensions
 * 
 * 2. a single {@link CqnAggregateTransformation aggregate} transformation is
 * specified -> the output set contains the aggregated values per dimension
 */
@Beta
public interface CqnGroupByTransformation extends CqnTransformation {

	/**
	 * Returns the dimensions by which the input set is grouped.
	 * 
	 * @return the dimensions by which the input set is grouped.
	 */
	List dimensions();

	/**
	 * Returns the pipeline of transformations, which is applied to the grouped
	 * input set.
	 * 
	 * @return the pipeline of transformations
	 */
	default List transformations() {
		return List.of();
	}

	@Override
	default Kind kind() {
		return Kind.GROUPBY;
	}
}