Hi
Assume SalesLines table and Reasons table have a common field SalesLines, count distinct SalesLines values in SalesLines table should be more than one in Reasons table. Then you want to get a merged table which will list both SalesLines have reasons or not, right?
On Power BI Desktop side, you can use Merge Queries property to merge those two tables by Left outer Join.
If you want to do it on SSAS side, I would suggest you post a thread in SSAS forum.
Best Regards,
Qiuyun Yu