Oracle text search on multiple tables and joins

I have the following SQL statement.

select emp_no,dob,dept_no from v_depts
where catsearch (emp_no,'abc',NULL) > 0
or
catsearch (dept_no,'abc',NULL) > 0

where v_depts is a view.

Now I would like to add one or more tables as join so that I can do text search on columns e.g. employee_details contains employee information and I can join with emp_no

I have created index on employee_details table for emp_name column, however I am not able to join with v_depts to search because I modify my sql statement as

select a.emp_no,a.dob,a.dept_no from v_depts a left outer join employee_details b
on (a.emp_no = b.emp_no)
where catsearch (a.emp_no,'abc',NULL) > 0
or
catsearch (a.dept_no,'abc',NULL) > 0
or
catsearch (b.emp_name,'abc',NULL) > 0

it gives me error

ORA-20000: Oracle Text error:
DRG-10849: catsearch does not support functional invocation
DRG-10599: column is not indexed

even though I have created index for emp_name column in employee_details table. How can I solve this problem?

Index statement for emp_name

CREATE INDEX IDX_EMP_DETAILS ON EMPLOYEE_DETAILS(EMP_NAME)INDEXTYPE IS CTXSYS.CTXCAT

I usually solve fulltext searches on multiple columns on different tables by materializing a structured XML view of them and then creating the index on the whole XML.

This solution is generic and also give you freedom on search: the whole view or only a subpath. The drawback is managing the refresh of a MV who usually cannot be refreshed fast; but update of fulltext index usually isn't in real-time, too, so you can just schedulate it.

-- Crating the view
CREATE MATERIALIZED VIEW fulltext_helper
NOLOGGING
BUILD DEFERRED
REFRESH COMPLETE ON DEMAND
AS
SELECT 
   a.dob, -- we don't need to fulltext on him
   XMLELEMENT(helper,
     XMLFOREST(a.emp_no AS emp_no, 
              a.dept_no AS dept_no, 
              b.emp_name AS emp_name)
   ) AS indexme
FROM v_depts a 
LEFT OUTER JOIN employee_details b
ON (a.emp_no = b.emp_no);

-- Creating the index
BEGIN
    ctx_ddl.create_preference('fulltext_helper_lexer', 'BASIC_LEXER');
    ctx_ddl.create_preference('fulltext_helper_filter', 'NULL_FILTER');
END;
/
CREATE INDEX fulltext_helper_index ON fulltext_helper (indexme)
INDEXTYPE IS CTXSYS.CONTEXT PARAMETERS (
    'DATASTORE CTXSYS.DIRECT_DATASTORE
     LEXER fulltext_helper_lexer
     FILTER fulltext_helper_filter');

-- Searching the whole data
SELECT * FROM fulltext_helper
WHERE contains(indexme, '{abc} INPATH (/helper)') > 0;

-- Searching only on "empno"
SELECT * FROM fulltext_helper
WHERE contains(indexme, '{abc} INPATH (/helper/emp_no)') > 0;