Change columns for association (Table Join) - Nested Data doesnt pull anything

Pracrtise  app Objective: Page 1 – Lists all samples Page 2 – Should list all Test associated to sample row clicked on Page 1 Page 3 – Should show results associated to test   I created a new application from excel. It has three tables, and one common column between the first and second tables. Another common column between second and third. Mendix decides itself on which column join should be made.   How to change column for join, as with Nested Data it pulls nothing. I would want to join columns I imported from excel  
1 answers

“one common column between  first and second table. Another common column between second and third.”

Do you mean an association?