Ndata not returning all possible results

Question

i created an index with userdatastore, basic lexer and basic wordlist preferences. Also a section group with ndata section. base letter, substring index all are true.
but when i search for 'scri', i am not getting 'de*scri*ption' in the results. pls help.

Answer 1

Roger,
Since the original poster has not provided a test case, I threw one together based on the information provided and found a couple of surprising things. The first surprise is that "scri" appears in the indexed tokens, even though a search for it returns no rows. The second surprise is that you do not need to put curly brackets around "not" and "and" when used within ndata like you do with other queries; Just using a stoplist without them is sufficient. Please find my test script and execution below.
-- test script:
drop table table1
exec ctx_ddl.drop_section_group ('mystery_sg')
exec ctx_ddl.drop_preference ('mystery_wl')
exec ctx_ddl.drop_preference ('mystery_lex')
exec ctx_ddl.drop_preference ('mystery_ds')
-- table:
create table table1
  (column1         varchar2(60),
   indexed_column  varchar2(1))
-- test data:
insert all
into table1 values ('description', null)
into table1 values ('this not that', null)
into table1 values ('this and that', null)
select * from dual
-- procedure:
create or replace procedure mystery_proc
  (p_rowid in            rowid,
   p_clob  in out nocopy clob)
as
begin
  select '<tag1>' || column1 || '</tag1>'
  into   p_clob
  from   table1
  where  rowid = p_rowid;
end mystery_proc;
show errors
-- preferences:
begin
  ctx_ddl.create_preference ('mystery_ds', 'user_datastore');
  ctx_ddl.set_attribute ('mystery_ds', 'procedure', 'mystery_proc');
  ctx_ddl.create_preference ('mystery_lex', 'basic_lexer');
  ctx_ddl.set_attribute ('mystery_lex', 'base_letter', 'YES');
  ctx_ddl.create_preference ('mystery_wl', 'basic_wordlist');
  ctx_ddl.set_attribute ('mystery_wl', 'substring_index', 'true');
  ctx_ddl.create_section_group ('mystery_sg', 'basic_section_group');
  ctx_ddl.add_ndata_section ('mystery_sg', 'tag1', 'tag1');
end;
-- index:
create index test_idx
on table1 (indexed_column)
indextype is ctxsys.context
parameters
  ('datastore      mystery_ds
    lexer          mystery_lex
    wordlist       mystery_wl
    section group  mystery_sg
    stoplist       ctxsys.empty_stoplist')
-- tokens created by indexing:
select token_text from dr$test_idx$i
-- queries:
select column1, score(1) from table1
where  contains (indexed_column, 'ndata(tag1, scri)', 1) > 0
order  by score(1) desc
select column1, score(1) from table1
where  contains (indexed_column, 'ndata(tag1, escr)', 1) > 0
order  by score(1) desc
select column1, score(1) from table1
where  contains (indexed_column, 'ndata(tag1, not)', 1) > 0
order  by score(1) desc
select column1, score(1) from table1
where  contains (indexed_column, 'ndata(tag1, and)', 1) > 0
order  by score(1) desc
/-- execution:
SCOTT@orcl_11gR2> -- table:
SCOTT@orcl_11gR2> create table table1
  2    (column1      varchar2(60),
  3       indexed_column     varchar2(1))
  4  /
Table created.
SCOTT@orcl_11gR2> -- test data:
SCOTT@orcl_11gR2> insert all
  2  into table1 values ('description', null)
  3  into table1 values ('this not that', null)
  4  into table1 values ('this and that', null)
  5  select * from dual
  6  /
3 rows created.
SCOTT@orcl_11gR2> -- procedure:
SCOTT@orcl_11gR2> create or replace procedure mystery_proc
  2    (p_rowid in           rowid,
  3       p_clob     in out nocopy clob)
  4  as
  5  begin
  6    select '<tag1>' || column1 || '</tag1>'
  7    into   p_clob
  8    from   table1
  9    where  rowid = p_rowid;
10  end mystery_proc;
11  /
Procedure created.
SCOTT@orcl_11gR2> show errors
No errors.
SCOTT@orcl_11gR2> -- preferences:
SCOTT@orcl_11gR2> begin
  2    ctx_ddl.create_preference ('mystery_ds', 'user_datastore');
  3    ctx_ddl.set_attribute ('mystery_ds', 'procedure', 'mystery_proc');
  4    ctx_ddl.create_preference ('mystery_lex', 'basic_lexer');
  5    ctx_ddl.set_attribute ('mystery_lex', 'base_letter', 'YES');
  6    ctx_ddl.create_preference ('mystery_wl', 'basic_wordlist');
  7    ctx_ddl.set_attribute ('mystery_wl', 'substring_index', 'true');
  8    ctx_ddl.create_section_group ('mystery_sg', 'basic_section_group');
  9    ctx_ddl.add_ndata_section ('mystery_sg', 'tag1', 'tag1');
10  end;
11  /
PL/SQL procedure successfully completed.
SCOTT@orcl_11gR2> -- index:
SCOTT@orcl_11gR2> create index test_idx
  2  on table1 (indexed_column)
  3  indextype is ctxsys.context
  4  parameters
  5    ('datastore     mystery_ds
  6        lexer          mystery_lex
  7        wordlist     mystery_wl
  8        section group     mystery_sg
  9        stoplist     ctxsys.empty_stoplist')
10  /
Index created.
SCOTT@orcl_11gR2> -- tokens created by indexing:
SCOTT@orcl_11gR2> select token_text from dr$test_idx$i
  2  /
TOKEN_TEXT
^ad$
^an$
^and
^dec
^des
^dsc
^esc
^hat
^his
^nd$
^no$
^not
^nt$
^ot$
^tat
^tha
^thi
^ths
^tht
^tis
and$
cipt
crip
crit
crpt
decr
desc
desr
dscr
ecri
esci
escr
esri
hat$
his$
ion$
ipio
ipti
ipto
itio
not$
pion
ptin
ptio
pton
ripi
ript
riti
rpti
scip
scri
scrp
srip
tat$
tha$
that
thi$
this
ths$
tht$
tin$
tio$
tion
tis$
ton$
65 rows selected.
SCOTT@orcl_11gR2> -- queries:
SCOTT@orcl_11gR2> select column1, score(1) from table1
  2  where  contains (indexed_column, 'ndata(tag1, scri)', 1) > 0
  3  order  by score(1) desc
  4  /
no rows selected
SCOTT@orcl_11gR2> select column1, score(1) from table1
  2  where  contains (indexed_column, 'ndata(tag1, escr)', 1) > 0
  3  order  by score(1) desc
  4  /
COLUMN1                                                        SCORE(1)
description                                                          60
1 row selected.
SCOTT@orcl_11gR2> select column1, score(1) from table1
  2  where  contains (indexed_column, 'ndata(tag1, not)', 1) > 0
  3  order  by score(1) desc
  4  /
COLUMN1                                                        SCORE(1)
this not that                                                       100
1 row selected.
SCOTT@orcl_11gR2> select column1, score(1) from table1
  2  where  contains (indexed_column, 'ndata(tag1, and)', 1) > 0
  3  order  by score(1) desc
  4  /
COLUMN1                                                        SCORE(1)
this and that                                                       100
1 row selected.
SCOTT@orcl_11gR2>