create procedure restart_identity (
  p_tabschema varchar(128)
, p_tabname   varchar(128)
, out p_rc int
, out p_msg varchar(128)
, out p_stmt varchar(1024)
)
begin
 declare SQLCODE int default 0;
 declare l_max decfloat;
 declare l_colname varchar(128);
 declare c1 cursor for s1;
 declare exit handler for sqlexception
 begin
   GET DIAGNOSTICS EXCEPTION 1 p_msg = MESSAGE_TEXT;
   SET p_rc=SQLCODE;
 end;

 set p_rc=0;
 select 
   'select max(' || colname || ') + 1 from ' || p_tabschema || '.' || p_tabname 
 , colname
 into p_stmt, l_colname
 from syscat.columns
 where identity='Y'
 and tabschema = p_tabschema and tabname = p_tabname;
 
 if (sqlcode = 100) then
   set p_rc = -1, p_msg = 'No such table (' || p_tabschema || '.' || p_tabname || ') or no identity column';
   return;
 end if;

 prepare s1 from p_stmt;
 open c1;
 fetch c1 into l_max;
 close c1;

 set p_stmt = 'alter table '||p_tabschema||'.'||p_tabname||' alter '||l_colname||' restart with '||char(l_max);
 execute immediate p_stmt;
end@

call restart_identity('MYSCHEMA', 'MYTABLE', ?, ?, ?)@