WordPress at a glance
function is not described

Automattic\WooCommerce\Admin\API\Reports\Stock

Controller::add_wp_query_join() public WC 1.0

Join posts meta tables when product search or low stock query is present.

{} It's a method of the class: Controller{}

No Hooks.

Return

String. Nothing.

Usage

$result = Controller::add_wp_query_join( $join, $wp_query );
$join(string) (required)
Join clause used to search posts.
$wp_query(object) (required)
WP_Query object.

Code of Controller::add_wp_query_join() WC 5.3.0

<?php
public static function add_wp_query_join( $join, $wp_query ) {
	global $wpdb;

	$stock_status = $wp_query->get( 'stock_status' );
	if ( $stock_status ) {
		$join = self::append_product_sorting_table_join( $join );
	}

	if ( $wp_query->get( 'low_in_stock' ) ) {
		$join  = self::append_product_sorting_table_join( $join );
		$join .= " LEFT JOIN {$wpdb->postmeta} AS low_stock_amount_meta ON {$wpdb->posts}.ID = low_stock_amount_meta.post_id AND low_stock_amount_meta.meta_key = '_low_stock_amount' ";
	}

	return $join;
}