I have a form containing 2 tables

1 the teacher
2 the teacher positions

i would like to have the teacher positions in a grid
Up to this point i have no problem. The problem arises
when in this grid i have 2 columns

1 the teacher position
2 the description of the teachers positions

I have no problem with the teachers positions in the
first column but i do have a problem with the descriptions

The descriptions are stored into a 3rd table. I want this description to appear in the second column of my grid

THE QUESTION:

How does one show the description in the second column
based on the first column in the grid.