Source

File: wp-includes/class-wp-network-query.php

protected function get_network_ids() {
		global $wpdb;

		$order = $this->parse_order( $this->query_vars['order'] );

		// Disable ORDER BY with 'none', an empty array, or boolean false.
		if ( in_array( $this->query_vars['orderby'], array( 'none', array(), false ), true ) ) {
			$orderby = '';
		} elseif ( ! empty( $this->query_vars['orderby'] ) ) {
			$ordersby = is_array( $this->query_vars['orderby'] ) ?
				$this->query_vars['orderby'] :
				preg_split( '/[,\s]/', $this->query_vars['orderby'] );

			$orderby_array = array();
			foreach ( $ordersby as $_key => $_value ) {
				if ( ! $_value ) {
					continue;
				}

				if ( is_int( $_key ) ) {
					$_orderby = $_value;
					$_order   = $order;
				} else {
					$_orderby = $_key;
					$_order   = $_value;
				}

				$parsed = $this->parse_orderby( $_orderby );

				if ( ! $parsed ) {
					continue;
				}

				if ( 'network__in' === $_orderby ) {
					$orderby_array[] = $parsed;
					continue;
				}

				$orderby_array[] = $parsed . ' ' . $this->parse_order( $_order );
			}

			$orderby = implode( ', ', $orderby_array );
		} else {
			$orderby = "$wpdb->site.id $order";
		}

		$number = absint( $this->query_vars['number'] );
		$offset = absint( $this->query_vars['offset'] );
		$limits = '';

		if ( ! empty( $number ) ) {
			if ( $offset ) {
				$limits = 'LIMIT ' . $offset . ',' . $number;
			} else {
				$limits = 'LIMIT ' . $number;
			}
		}

		if ( $this->query_vars['count'] ) {
			$fields = 'COUNT(*)';
		} else {
			$fields = "$wpdb->site.id";
		}

		// Parse network IDs for an IN clause.
		if ( ! empty( $this->query_vars['network__in'] ) ) {
			$this->sql_clauses['where']['network__in'] = "$wpdb->site.id IN ( " . implode( ',', wp_parse_id_list( $this->query_vars['network__in'] ) ) . ' )';
		}

		// Parse network IDs for a NOT IN clause.
		if ( ! empty( $this->query_vars['network__not_in'] ) ) {
			$this->sql_clauses['where']['network__not_in'] = "$wpdb->site.id NOT IN ( " . implode( ',', wp_parse_id_list( $this->query_vars['network__not_in'] ) ) . ' )';
		}

		if ( ! empty( $this->query_vars['domain'] ) ) {
			$this->sql_clauses['where']['domain'] = $wpdb->prepare( "$wpdb->site.domain = %s", $this->query_vars['domain'] );
		}

		// Parse network domain for an IN clause.
		if ( is_array( $this->query_vars['domain__in'] ) ) {
			$this->sql_clauses['where']['domain__in'] = "$wpdb->site.domain IN ( '" . implode( "', '", $wpdb->_escape( $this->query_vars['domain__in'] ) ) . "' )";
		}

		// Parse network domain for a NOT IN clause.
		if ( is_array( $this->query_vars['domain__not_in'] ) ) {
			$this->sql_clauses['where']['domain__not_in'] = "$wpdb->site.domain NOT IN ( '" . implode( "', '", $wpdb->_escape( $this->query_vars['domain__not_in'] ) ) . "' )";
		}

		if ( ! empty( $this->query_vars['path'] ) ) {
			$this->sql_clauses['where']['path'] = $wpdb->prepare( "$wpdb->site.path = %s", $this->query_vars['path'] );
		}

		// Parse network path for an IN clause.
		if ( is_array( $this->query_vars['path__in'] ) ) {
			$this->sql_clauses['where']['path__in'] = "$wpdb->site.path IN ( '" . implode( "', '", $wpdb->_escape( $this->query_vars['path__in'] ) ) . "' )";
		}

		// Parse network path for a NOT IN clause.
		if ( is_array( $this->query_vars['path__not_in'] ) ) {
			$this->sql_clauses['where']['path__not_in'] = "$wpdb->site.path NOT IN ( '" . implode( "', '", $wpdb->_escape( $this->query_vars['path__not_in'] ) ) . "' )";
		}

		// Falsey search strings are ignored.
		if ( strlen( $this->query_vars['search'] ) ) {
			$this->sql_clauses['where']['search'] = $this->get_search_sql(
				$this->query_vars['search'],
				array( "$wpdb->site.domain", "$wpdb->site.path" )
			);
		}

		$join = '';

		$where = implode( ' AND ', $this->sql_clauses['where'] );

		$groupby = '';

		$pieces = array( 'fields', 'join', 'where', 'orderby', 'limits', 'groupby' );

		/**
		 * Filters the network query clauses.
		 *
		 * @since 4.6.0
		 *
		 * @param string[]         $pieces An associative array of network query clauses.
		 * @param WP_Network_Query $this   Current instance of WP_Network_Query (passed by reference).
		 */
		$clauses = apply_filters_ref_array( 'networks_clauses', array( compact( $pieces ), &$this ) );

		$fields  = isset( $clauses['fields'] ) ? $clauses['fields'] : '';
		$join    = isset( $clauses['join'] ) ? $clauses['join'] : '';
		$where   = isset( $clauses['where'] ) ? $clauses['where'] : '';
		$orderby = isset( $clauses['orderby'] ) ? $clauses['orderby'] : '';
		$limits  = isset( $clauses['limits'] ) ? $clauses['limits'] : '';
		$groupby = isset( $clauses['groupby'] ) ? $clauses['groupby'] : '';

		if ( $where ) {
			$where = 'WHERE ' . $where;
		}

		if ( $groupby ) {
			$groupby = 'GROUP BY ' . $groupby;
		}

		if ( $orderby ) {
			$orderby = "ORDER BY $orderby";
		}

		$found_rows = '';
		if ( ! $this->query_vars['no_found_rows'] ) {
			$found_rows = 'SQL_CALC_FOUND_ROWS';
		}

		$this->sql_clauses['select']  = "SELECT $found_rows $fields";
		$this->sql_clauses['from']    = "FROM $wpdb->site $join";
		$this->sql_clauses['groupby'] = $groupby;
		$this->sql_clauses['orderby'] = $orderby;
		$this->sql_clauses['limits']  = $limits;

		$this->request = "{$this->sql_clauses['select']} {$this->sql_clauses['from']} {$where} {$this->sql_clauses['groupby']} {$this->sql_clauses['orderby']} {$this->sql_clauses['limits']}";

		if ( $this->query_vars['count'] ) {
			return intval( $wpdb->get_var( $this->request ) );
		}

		$network_ids = $wpdb->get_col( $this->request );

		return array_map( 'intval', $network_ids );
	}