All value of dimension for one expression in concat

[sophie_bd]

Hello,

i want to display all the value for all dimension in a concat : 

- concat for dimension  : concat(distinct code_sous_traitant,'/',code_sous_traitant) => result AAA/BBBB

- concat for expression : concat(distinct aggr($(v_Encours_AttendusSAV_EEversSTT_DernierJour),code_sous_traitant),'/',code_sous_traitant) => 12 (if BBBB or AAA had no value)

How to show 12/0 in the result of expression ?

Thanks for your help,

Sophie