Dax with Many to Many

1.Create a Bridge Table (SalesPerson–Promotion pairs).

Relate it to both Sales and Promotions.

2.Use TREATAS to filter only salespeople in that promotion.

Sales_XDaysBefore =
CALCULATE(
SUM(Sales[SalesAmount]),
TREATAS(VALUES(PromotionParticipants[SalesPersonID]), Sales[SalesPersonID]),
DATESBETWEEN(
'Date'[Date],
MAX(Promotions[PromotionDate]) - X,
MAX(Promotions[PromotionDate]) - 1
)
)

Same pattern for After X Days (just shift the date range forward).

Build measures for 30/60/90 days → Compare Before vs After → compute Lift %.

👉 Bridge + TREATAS is the key to handle many-to-many.