When adding a column to a table in a model, it is possible to drag the column from the source system tree, into the diagram in the middle pane.
To add columns...

  1. Click on a column and drag it into the table in the diagram.
  2. The following dialog will ask you to confirm the addition of the selected column. Click OK.
  3. The column has been added to the table in the diagram.

It is possible to drag more than one column at a time, as long as the columns are within the same table in the source system tree.