with a(tab, rn) as (
select rtrim(t.tabschema)||'.'||t.tabname tab, rownumber() over() rn
from syscat.tables t
join syscat.columns c on t.tabschema=c.tabschema and t.tabname=c.tabname
where c.colname='WRITETIME' and t.type='T'
)
, b(stmt, rn) as (
select cast('select '''||tab||''', max(WRITETIME) from '||tab as clob(32k)), rn from a where rn= 1 
  union all
select b.stmt||' union all select '''||tab||''', max(WRITETIME) from '||a.tab, a.rn from a, b where a.rn=b.rn+ 1 
)
select 'select * from ('||stmt||') t(tab, WRITETIME)' from b where rn=(select max(rn) from a)

insert into session.t (tabname, writetime) select 'tab', max(writetime) from tab

create procedure get_max()
dynamic result sets  1 
begin
  declare stmt varchar( 4000 );
  declare c1 cursor with return for s1;

  set stmt = 
    'declare global temporary table session.t(TAB varchar(128) not null, WRITETIME timestamp) '
  ||'with replace not logged';
  execute immediate stmt;

  for v as 
    select rtrim(t.tabschema)||'.'||t.tabname tab
    from syscat.tables t
    join syscat.columns c on t.tabschema=c.tabschema and t.tabname=c.tabname
    where c.colname='WRITETIME' and t.type='T'
  do
     set stmt = 'insert into session.t select '''||v.tab||''', max(WRITETIME) from '||tab;
     execute immediate stmt;
  end for;

  set stmt='select * from session.t';
  prepare s1 from stmt;
  open c1;
end@

select rtrim(t.tabschema)||'.'||t.tabname tab
select '"'||rtrim(t.tabschema)||'"."'||t.tabname||'"' tab

select '"'||replace(rtrim(t.tabschema), '"', '""')||'"."'||replace(t.tabname, '"', '""')||'"' tab