External table - fetch location ?

Question

Using Oracle 10.2.0.5
An external table is a construct that gives me SQL access to a file.
Is it possible to know the name of the file somehow inside the select? Like Add a column with the file name?
pseudo example
CREATE TABLE EXT_DUMMY
    "RECORDTYPE" VARCHAR2(100 BYTE),
    "COL1" VARCHAR2(100 BYTE),
    "COL2" VARCHAR2(100 BYTE),
    "FILE" VARCHAR2(100 BYTE)
ORGANIZATION EXTERNAL
    TYPE ORACLE_LOADER DEFAULT DIRECTORY "IMPORT_BAD_FILE"
    ACCESS PARAMETERS (
             records delimited BY newline
             FIELDS TERMINATED BY ';'
             MISSING FIELD VALUES ARE NULL
               ( RECORDTYPE CHAR
               , COL1 CHAR
               , COL2 CHAR
               , FILE CHAR FILLER
    LOCATION ( 'Testfile1.txt, Testfile2.txt' )
    reject limit 10
;The result could look like this:
RECORDTYPE   COL1       COL2      FILE
SAMPLE           DUMMY    DUMMY Testfile1.txt
SAMPLE           DUMMY1   DUMMY Testfile1.txt
SAMPLE           DUMMY2   DUMMY Testfile1.txt
SAMPLE           DUMMY3   DUMMY Testfile1.txt
SAMPLE           DUMMY1   DUMMY1 Testfile2.txt
SAMPLE           DUMMY1   DUMMY2 Testfile2.txt
SAMPLE           DUMMY2   DUMMY1 Testfile2.txtI would like to know from which file a certain row is read. Maybe I missed an option in the documentation. In this example I have two different files as the source for the external table.
Another use case could be this:
If I enable a user to switch the external table to a different file alter table EXT_DUMMY location ('Testfile3.txt' ). How can we know which file is read during the select on the table? When userA does the select, maybe userB just altered the location before the select was started. Therefore userA would read in a different file then expected.
Edited by: Sven W. on May 26, 2011 4:48 PM
Edited by: Sven W. on May 26, 2011 4:51 PM
Edited by: Sven W. on May 26, 2011 5:11 PM

Answer 1

Hi Sven,
I'm not sure how much we can rely on this, but let's consider the following :
create table test_xt (
  rec_id  number
, message varchar2(100)
organization external (
  default directory test_dir
  access parameters (
    records delimited by newline
    fields terminated by ';'
  location (
    'marc5.txt'
  , 'test1.csv'
  , 'test2.csv'
  , 'test3.csv'
);I always thought the ROWID doesn't hold much sense for an external table, but...
SQL> select t.rowid
  2       , dump(t.rowid) as rowid_dump
  3       , regexp_substr(dump(t.rowid,10,9,1),'\d+$') as file#
  4       , t.*
  5  from test_xt t
  6  ;
ROWID              ROWID_DUMP                                                FILE#      REC_ID MESSAGE
(AADVyAAAAAAAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,0,0,0,0,0,0,0,0,0     0               1 this is a line from marc5.txt
(AADVyAAAAAAAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,0,0,0,0,0,0,0,0,33    0               2 this is a line from marc5.txt
(AADVyAAAAAAAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,0,0,0,0,0,0,0,0,66    0               3 this is a line from marc5.txt
(AADVyAAAAAAAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,0,0,0,0,0,0,0,0,99    0               4 this is a line from marc5.txt
(AADVyAAAAAEAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,1,0,0,0,0,0,0,0,0     1               1 this is a line from test1.csv
(AADVyAAAAAEAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,1,0,0,0,0,0,0,0,33    1               2 this is a line from test1.csv
(AADVyAAAAAEAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,1,0,0,0,0,0,0,0,66    1               3 this is a line from test1.csv
(AADVyAAAAAEAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,1,0,0,0,0,0,0,0,99    1               4 this is a line from test1.csv
(AADVyAAAAAIAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,2,0,0,0,0,0,0,0,0     2               1 this is a line from test2.csv
(AADVyAAAAAIAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,2,0,0,0,0,0,0,0,33    2               2 this is a line from test2.csv
(AADVyAAAAAIAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,2,0,0,0,0,0,0,0,66    2               3 this is a line from test2.csv
(AADVyAAAAAMAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,3,0,0,0,0,0,0,0,0     3               1 this is a line from test3.csv
(AADVyAAAAAMAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,3,0,0,0,0,0,0,0,33    3               2 this is a line from test3.csv
(AADVyAAAAAMAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,3,0,0,0,0,0,0,0,66    3               3 this is a line from test3.csv
(AADVyAAAAAMAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,3,0,0,0,0,0,0,0,99    3               4 this is a line from test3.csv
(AADVyAAAAAMAAAAAA Typ=208 Len=17: 4,0,0,213,200,0,0,0,3,0,0,0,0,0,0,0,132   3               5 this is a line from test3.csv
16 rows selected
Then with a join to EXTERNAL_LOCATION$ :
SQL> with ext_loc as (
  2    select position-1 as pos
  3         , name as filename
  4    from sys.external_location$
  5    where obj# = ( select object_id
  6                   from user_objects
  7                   where object_name = 'TEST_XT' )
  8  )
  9  select x.filename,
10         t.*
11  from test_xt t
12       join ext_loc x on x.pos = to_number(regexp_substr(dump(t.rowid,10,9,1),'\d+$'))
13  ;
FILENAME       REC_ID MESSAGE
marc5.txt           1 this is a line from marc5.txt
marc5.txt           2 this is a line from marc5.txt
marc5.txt           3 this is a line from marc5.txt
marc5.txt           4 this is a line from marc5.txt
test1.csv           1 this is a line from test1.csv
test1.csv           2 this is a line from test1.csv
test1.csv           3 this is a line from test1.csv
test1.csv           4 this is a line from test1.csv
test2.csv           1 this is a line from test2.csv
test2.csv           2 this is a line from test2.csv
test2.csv           3 this is a line from test2.csv
test3.csv           1 this is a line from test3.csv
test3.csv           2 this is a line from test3.csv
test3.csv           3 this is a line from test3.csv
test3.csv           4 this is a line from test3.csv
test3.csv           5 this is a line from test3.csv
Seems to work... assuming the files are always read in the order specified through the LOCATION parameter, and the generated ROWID actually means what I think it means.