Oracle‘s rowid

select col_1, col_2, **rowid** from some_table

A rowid identifies a row in a table

A rowid is a pseudo column (like versions_xid), that uniquely identifies a row within a table, but not within a database. It is possible for two rows of two different tables stored in the

Using dbms_rowid

In order to find the datafile, block number and slot number, dbms_rowid can be used:

set serveroutput on size 1000000 format wrapped

create table rowid_test (
  id      number,
  dummy1  varchar2(4000),
  dummy2  varchar2(4000),
  dummy3  varchar2(4000),
  dummy4  varchar2(4000)
);

begin
  for i in 1 .. 400 loop
    insert into rowid_test values(i, 
      lpad('1', i, '1'),
      lpad('2', i, '2'),
      lpad('3', i, '3'),
      lpad('4', i, '4'));
  end loop;
  
  -- delete but every 20th record
  delete from rowid_test where mod(id,20) <> 0;
end;
/


declare
  r          rowid;
  i          number := 1;
  v_filename dba_data_files.file_name%type;
begin
  for p in (
    select
      rowid 
    from 
      rowid_test
    ) loop

     select
       file_name
     into 
       v_filename
     from 
       dba_data_files
     where
       file_id = dbms_rowid.rowid_relative_fno(p.rowid);


     dbms_output.put_line('row no    : ' || i         );
     dbms_output.put_line('  file    : ' || v_filename);
     dbms_output.put_line('  block no: ' || dbms_rowid.rowid_block_number(p.rowid));
     dbms_output.put_line('  slot no : ' || dbms_rowid.rowid_row_number(p.rowid));
     dbms_output.put_line('');

    i := i+1;
  end loop;
end;
/

drop table rowid_test;




row no    : 1
  file    : D:\ORACLE\DATABASES\ORA10\DATA.DBF
  block no: 3890
  slot no : 19

row no    : 2
  file    : D:\ORACLE\DATABASES\ORA10\DATA.DBF
  block no: 3890
  slot no : 39

  [....]

Bigfile rowids

A bigfile tablespace can only have on datafile associated with it, therefor, the three bytes that identified the datafile can now additionally be used to address db blocks.

'Changing' rowids

Although a rowid uniquely identifies a row in a table, it might change its value if the underlying table is an index organized table or a partitioned table.

Also, rowids change if a table is exported and imported using EXP/IMP.

This implies that rowids should not be stored away for later re-use as the corresponding row then might either not exist or contain completely different data.

Misc

Getting the block number (within a segment from a rowid:

select dbms_rowid.rowid_block_number(rowid) from t where ....