How to implement multiselect rows in a Web Dynpro UI Element Table

I have a Table containing one coulmn(type: String) and 3 rows. I have created action Select. Even SelectionMode property of Table is set to "Multi".

The rows have a data of "1" , "2" ,"3" respectively.

I want the above values to be concatenated and I should get "123" as output from the action.

Can anyone help me how to achieve this?