execute block returns (s varchar( 20080 ))
as
declare i int;
begin
  s = 'create table t (id int)';
  execute statement :s;
  suspend;

  s = '';
  i =  1 ;
  while (i <  1000 ) do
  begin
    if (char_length(s) <  20000  or s = '')
    then begin
      if (s = '')
      then s = 'alter table t add col' || i || ' int';
      else s = s || ', add col' || i || ' int';
    end
    else begin
      execute statement :s;
      suspend;

      s = '';
    end

    i = i +  1 ;
  end

  if (s <> '')
  then begin
    execute statement :s;
    suspend;
  end
end;
commit;

execute block as
declare i int =  0 ;
begin
  while (i <  1000000 ) do
  begin
    insert into t (id) values (:i);
    i = i +  1 ;
  end
end
commit;

Data pages: 14085, data page slots: 14085, average fill: 79%
Average record length: 73.93, total records: 1000000

update t set col999 =  1 

    Average record length: 77.26, total records: 1000000 
    Data pages: 16796, data page slots: 16796, average fill: 98% 

SQL> create table EmptyTable
   2   (RecordId integer,
   3   ColId integer,
   4   CalValue integer)
   5   storage(initial 1M next  0 );

Table created.

SQL> insert into EmptyTable(RecordId,ColId,CalValue)
   2   select n, 1000 , 1  from (select rownum n from dual connect by level <  1000001 );

 1000000  rows created.

SQL> select bytes/ 1024 / 1024  from dba_segments where segment_name=upper('EmptyTable');

BYTES/ 1024 / 1024 
---------------
              18 

SQL> create table EmptyTable
   2   (RecordId integer,
   3   ColId integer,
   4   CalValue integer)
   5   storage(initial 1M next  0 );

Table created.

SQL> insert into EmptyTable(RecordId,ColId,CalValue)
   2   select n, 1000 , 1  from (select rownum n from dual connect by level <  1000001 );

 1000000  rows created.

SQL> select bytes/ 1024 / 1024  from dba_segments where segment_name=upper('EmptyTable');

BYTES/ 1024 / 1024 
---------------
              18