groupBy(groupList) {
		if (!Array.isArray(groupList)) {
			throw new SyntaxError(`groupBy() parameter 1 should be an array, ${typeof groupList} given.`);
		}

		this._query.groupBy = groupList.join(', ');
		return this;
	}
/**
	 * assigns multiple group by columns
	 * @param {array} groupList
	 */
assigns multiple group by columns
@param {array} groupList
assigns multiple group by columns @param { array } groupList
groupBy(groupList) {
		if (!Array.isArray(groupList)) {
			throw new SyntaxError(`groupBy() parameter 1 should be an array, ${typeof groupList} given.`);
		}
		this._query.groupBy = groupList.join(', ');
		return this;
	}
groupBy ( groupList ) { if ( ! Array . isArray ( groupList ) ) { throw new SyntaxError ( ` ${ typeof groupList } ` ) ; } this . _query . groupBy = groupList . join ( ', ' ) ; return this ; }
assigns multiple group by columns
 @param {array} groupList
assigns multiple group by columns @param { array } groupList