I assume that you won't use the 6 million rows individually. How about setting a stored procedure as the source of a pivot table in Excel?
There's no way that...

What about using something like this?

SELECT TOP (1) PERCENT *
FROM MyTable;

Note that if you add an ORDER BY clause the performance will decrease.

I agree with franz, this will be slow. I´m not sure about the performance of the TRANSLATE function (MS has done terrible things with FORMAT), but here's a much faster...

Needed some coffee before answering. I thought it was asking for the result of
SELECT * FROM #tempout
:Wow:

You can find lots of resources on the internet about tempdb best practices.
Here's one: https://www.brentozar.com/archive/2016/01/cheat-sheet-how-to-configure-tempdb-for-microsoft-sql-server/

You might have some unintended cross joins. Try to pre-aggregate your values.

SELECT _MDT.codiceMandato as Customer,
  SUM(FM.Revenue) AS Revenue,
  SUM(PG.Paid) AS Paid
FROM (SELECT _PG.idMandato,...

I'm sure that this can be done with Oracle, but that's not how SQL Server cursors work.
Why would you want to learn the wrong way of doing things instead...

What if you create a view and just use the view as your source?

CREATE VIEW dbo.vDIM_PRODUCT_GROUP
AS
  SELECT ID,
   PARENT_ID,
   ...