custom SQL query visualizacion in backend menu

You will have to edit the file "listing" of the view "product" of the back end for your back end template via the menu Display->Views.
There, add a query to load the sum for each product and display it in the listing.

Doing it via the Display->Views will create an override and you won't loose your changes when you update HikaShop.

Hi,

If you want a listing of the products with their sales count, you can do that now with either a report (menu Orders->Reports) or with a mass action (menu System>Mass actions).
With mass actions, you can simply have an action "display the results" with the columns product_name and product_sales selected and click on "process".
With reports, you can go further with filtering for only a period of time, only some categories, etc.

Hi,

Within a mass action it will be difficult to link the "product" with the "orders" though the "order products".
In that case it will be easier to have a custom plugin for your specific SQL query.

And with HikaShop 3, the new dashboard system allow to create reports via plugins.
That system is more flexible than the current Report system in HikaShop 2.x (and we will be able to create a bridge to also provide a nice easy interface to create simple reports) ; it gives you a possibility to write your own SQL to retrieve the data you want (and to perform the table link you need).

Now with your current request, you have to be careful on the fact that the number of column is dynamic.
More orders you will have for a products, more column it will display.

Regards,