Could you describe by English?
Or, show sample source data and expected results.

Assuming you want to count the number of rows in each table that have
matching values for a single column (num_cli), you have the following to do:
1. get counts for each table
2. merge the results

This is complicated by the possibility of having non-matching values in
num_cli for the tables. Application data rules may simplify this - ie.
the voiture table cannot have a num_cli that does NOT exist in poste.

The following query (UDB 8.2) will generate your results, assuming
non-matching values in both tables. T1 and t2 are your two tables and
"num" is the matching column:

with temp1 as (select num as num1,count(*) as count1
                 from t1 group by num),
     temp2 as (select num as num2, count(*) as count2
                 from t2 group by num),
     temp3 as (      select num1 as num from temp1
               union select num2 as num from temp2)
select num
      ,value(count1,0)    as "nombre de poste"
      ,coalesce(count2,0) as "nombre de voiture"
  from temp3
  left outer join temp1 on num = num1
  left outer join temp2 on num = num2
 order by num
;

source data:
insert into t1 values(1),(1),(2),(3),(3),(3),(4),(4),(5)
insert into t2 values(1),(1),(1),(3),(3),(3),(4),(5),(5),(6),(6)

results:

NUM         nombre de poste nombre de voiture
----------- --------------- -----------------
          1               2                 3
          2               1                 0
          3               3                 3
          4               2                 1
          5               1                 2
          6               0                 2

  6 record(s) selected.

Phil Sherman