I have created one Product list which contains "title" and "brand" column. I have created the query for "title" and "brand" in the content search web part by using a query string.
If I pass some value in the query string then the items are displaying in the content search web part.
Like if I access URL: https://mydomain.sharepoint.com/sites/abc/product.aspx?brand=mobile Then it is displaying the result in a content search web part.
When I am not passing any query string value then the results are not coming.
My requirement here is if no query string value then it should show all the items from the list and if some value is there then it should show items belongs to that particular item.
Means when I access https://mydomain.sharepoint.com/sites/abc/product.aspx URL it should show all the items from the list.
Currently, I am using "RefinableString03:{QueryString.brand}" query in the content search web part.