Oracles 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 wrappedcreate 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 : 19row 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 ....
