Question

In Oracle Database 10g and Oracle Database Express Edition 11g I have encountered some strange behavior. I have a column that is indexed as a ctxsys.context type index. When I query the table for results with a contains function, it works except when the value I’m searching for is ‘Still’. Then it returns no results. When I search for the same data with a column like ‘Still’ I get results normally. If I search for ‘Jazz’ using contains, then I get results normally.

Below is sql I used for reproducing this behavior on a newly created test table.

-- Setup the table with an index and some data
create table "STILL_TEST" (
    "ID" number(22,0) primary key,
    "PROF_DATA_15" varchar2(255 char),
    "OTHER" varchar2(255 char),
    "SHORTER" varchar2(100 char)
);
insert into "STILL_TEST" values (1, 'Still', 'Still', 'Still');
insert into "STILL_TEST" values (3, 'Jazz', 'Jazz', 'Jazz');
CREATE INDEX "STILL_TEST_PROF_DATA_15" ON "STILL_TEST" ("PROF_DATA_15")
   INDEXTYPE IS "CTXSYS"."CONTEXT" PARAMETERS ('SYNC (ON COMMIT)');
commit;

-- Now query it a bit. See how both types of queries work if the
-- parameter is 'Jazz'
select * from "STILL_TEST" where prof_data_15 like 'Jazz';
select * from "STILL_TEST" where contains(prof_data_15, 'Jazz') > 0;
select * from "STILL_TEST" where prof_data_15 like 'Still';
-- So far so good, but why doesn't this next query return any results?
select * from "STILL_TEST" where contains(prof_data_15, 'Still') > 0;

Answer 1

It seems the default stop list is at fault here. If the index is created using an empty stop list, then ‘still’ and other keywords will be treated as search parameters.

Following creates the index with an empty stop list:

 CREATE INDEX "STILL_TEST_PROF_DATA_15" ON "STILL_TEST" ("PROF_DATA_15")
 INDEXTYPE IS "CTXSYS"."CONTEXT" PARAMETERS ('STOPLIST CTXSYS.EMPTY_STOPLIST');

Here are some links to more info on stop lists:

http://docs.oracle.com/cd/A91202_01/901_doc/text.901/a90121/cdatadi9.htm

http://docs.oracle.com/cd/A91202_01/901_doc/text.901/a90121/astopsu2.htm#43324

Strangely enough, the word ‘still’ doesn’t appear in the default stop list according to the link above.