with a (name, rn_) as (
select '"'||tabschema||'"."'||tabname||'"', rownumber() over()
from syscat.tables
where type in ('T', 'S')
-- фильтр на таблицы, если надо:
and tabschema not like 'SYS%'
fetch first 10 rows only
)
, b (ord, str) as (
select 1
,   case when rn_=1 then 'select sum(cnt) from (' else ' union all' end
  ||' select count(1) cnt from '||name as str
from a
  union all
values (2, ') t(cnt) with ur;')
)
select str
from b
order by ord;