er_by_clause = '';

		$sql_query->clear_sql_clause( array( 'order_by' ) );
		if ( isset( $query_args['orderby'] ) ) {
			$order_by_clause = $this->normalize_order_by( $query_args['orderby'] );
			$sql_query->add_sql_clause( 'order_by', $order_by_clause );
		}

		// Return ORDER BY clause to allow adding the sort field(s) to query via a JOIN.
		return $order_by_clause;
	}

	/**
	 * Add order by order SQL clause.
	 *
	 * @param array    $query_args Parameters supplied by the user.
	 * @param SqlQuery $sql_query  Query object.
	 */
	protected function add_orderby_order_clause( $query_args, &$sql_query ) {
		if ( isset( $query_args['order'] ) ) {
			$sql_query->add_sql_clause( 'order_by', $query_args['order'] );
		} else {
			$sql_query->add_sql_clause( 'order_by', 'DESC' );
		}
	}

	/**
	 * Returns customer subquery to be used in WHERE SQL query, based on query arguments from the user.
	 *
	 * @param array $query_args Parameters supplied by the user.
	 * @return string
	 */
	protected function get_customer_subquery( $query_args ) {
		global $wpdb;

		$customer_filter = '';
		if ( isset( $query_args['customer_type'] ) ) {
			if ( 'new' === strtolower( $query_args['customer_type'] ) ) {
				$customer_filter = " {$wpdb->prefix}wc_order_stats.returning_customer = 0";
			} elseif ( 'returning' === strtolower( $query_args['customer_type'] ) ) {
				$customer_filter = " {$wpdb->prefix}wc_order_stats.returning_customer = 1";
			}
		}

		return $customer_filter;
	}

	/**
	 * Returns product attribute subquery elements used in JOIN and WHERE clauses,
	 * based on query arguments from the user.
	 *
	 * @param array $query_args Parameters supplied by the user.
	 * @return array
	 */
	protected function get_attribute_subqueries( $query_args ) {
		global $wpdb;

		$sql_clauses           = array(
			'join'  => array(),
			'where' => array(),
		);
		$match_operator        = $this->get_match_operator( $query_args );
		$join_table            = $wpdb->prefix . 'wc_order_product_lookup';
		$post_meta_comparators = array(
			'='  => 'attribute_is',
			'!=' => 'attribute_is_not',
		);

		foreach ( $post_meta_comparators as $comparator => $arg ) {
			if ( ! isset( $query_args[ $arg ] ) || ! is_array( $query_args[ $arg ] ) ) {
				continue;
			}
			foreach ( $query_args[ $arg ] as $attribute_term ) {
				// We expect tuples.
				if ( ! is_array( $attribute_term ) || 2 !== count( $attribute_term ) ) {
					continue;
				}

				// If the tuple is numeric, assume these are IDs.
				if ( is_numeric( $attribute_term[0] ) && is_numeric( $attribute_term[1] ) ) {
					$attribute_id = intval( $attribute_term[0] );
					$term_id      = intval( $attribute_term[1] );

					// Invalid IDs.
					if ( 0 === $attribute_id || 0 === $term_id ) {
						continue;
					}

					// @todo: Use wc_get_attribute() instead ?
					$attr_taxonomy = wc_attribute_taxonomy_name_by_id( $attribute_id );
					// Invalid attribute ID.
					if ( empty( $attr_taxonomy ) ) {
						continue;
					}

					$attr_term = get_term_by( 'id', $term_id, $attr_taxonomy );
					// Invalid term ID.
					if ( false === $attr_term ) {
						continue;
					}

					$meta_key   = wc_variation_attribute_name( $attr_taxonomy );
					$meta_value = $attr_term->slug;
				} else {
					// Assume these are a custom attribute slug/value pair.
					$meta_key   = 'attribute_' . esc_sql( $attribute_term[0] );
					$meta_value = esc_sql( $attribute_term[1] );
				}

				$join_alias = 'wpm1';

				// If we're matching all filters (AND), we'll need multiple JOINs on postmeta.
				// If not, just one.
				if ( 'AND' === $match_operator || empty( $sql_clauses['join'] ) ) {
					$join_idx              = count( $sql_clauses['join'] ) + 1;
					$join_alias            = 'wpm' . $join_idx;
					$sql_clauses['join'][] = "JOIN {$wpdb->postmeta} as {$join_alias} ON {$join_alias}.post_id = {$join_table}.variation_id";
				}

				// phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
				$sql_clauses['where'][] = $wpdb->prepare( "( {$join_alias}.meta_key = %s AND {$join_alias}.meta_value {$comparator} %s )", $meta_key, $meta_value );
			}
		}

		return $sql_clauses;
	}

	/**
	 * Returns logic operator for WHERE subclause based on 'match' query argument.
	 *
	 * @param array $query_args Parameters supplied by the user.
	 * @return string
	 */
	protected function get_match_operator( $query_args ) {
		$operator = 'AND';

		if ( ! isset( $query_args['match'] ) ) {
			return $operator;
		}

		if ( 'all' === strtolower( $query_args['match'] ) ) {
			$operator = 'AND';
		} elseif ( 'any' === strtolower( $query_args['match'] ) ) {
			$operator = 'OR';
		}
		return $operator;
	}

	/**
	 * Returns filtered comma separated ids, based on query arguments from the user.
	 *
	 * @param array  $query_args Parameters supplied by the user.
	 * @param string $field      Query field to filter.
	 * @param string $separator  Field separator.
	 * @return string
	 */
	protected function get_filtered_ids( $query_args, $field, $separator = ',' ) {
		$ids_str = '';
		$ids     = isset( $query_args[ $field ] ) && is_array( $query_args[ $field ] ) ? $query_args[ $field ] : array();

		/**
		 * Filter the IDs before retrieving report data.
		 *
		 * Allows filtering of the objects included or excluded from reports.
		 *
		 * @param array  $ids        List of object Ids.
		 * @param array  $query_args The original arguments for the request.
		 * @param string $field      The object type.
		 * @param string $context    The data store context.
		 */
		$ids = apply_filters( 'woocommerce_analytics_' . $field, $ids, $query_args, $field, $this->context );

		if ( ! empty( $ids ) ) {
			$ids_str = implode( $separator, $ids );
		}
		return $ids_str;
	}

	/**
	 * Assign report columns once full table name has been assigned.
	 */
	protected function assign_report_columns() {}
}