create table demo pctfree 0 as with q as (select 42 x from dual union all select 42 from dual) select 42 x from q a cross join q b cross join q c cross join q d cross join q e cross join q f cross join q g cross join q h cross join q i cross join q j cross join q k cross join q l cross join q m cross join q n cross join q o cross join q p cross join q r cross join q s cross join q t cross join q u

select dbms_xplan.format_size(bytes) "size" from user_segments where segment_name='DEMO'

-- adding a column does not add space :) alter table demo add b numeric ;

select dbms_xplan.format_size(bytes) "size" from user_segments where segment_name='DEMO'

-- even with a default value in it :)) alter table demo add c numeric default 42 not null;

select dbms_xplan.format_size(bytes) "size" from user_segments where segment_name='DEMO'

-- proof that table would grow if it updates the rows update demo set b=42;

select dbms_xplan.format_size(bytes) "size" from user_segments where segment_name='DEMO'

-- proof that table would grow if it updates the rows update demo set b=43/3;

select dbms_xplan.format_size(bytes) "size" from user_segments where segment_name='DEMO'