How to modify column data-type while column is in used - oracle

Question

I have problem while I use SELECT query. Unfortunettly, the ID is store as VARCHAR which is big mistake and right now I have problem in following function
FUNCTION GET_SUB_PROJECTS(p_currentUserId IN VARCHAR,p_projectId IN INT)
RETURN SYS_REFCURSOR IS
rc SYS_REFCURSOR;
-- getSubProject
BEGIN
OPEN rc FOR
SELECT
p.*,
a.number_ AS activityNumber,
a.description AS activityDescription
FROM
projects p
LEFT JOIN
project_users_schedule_dates pusd
ON
pusd.ProjectID = p.ProjectID AND pusd.UserID = p_currentUserId
LEFT JOIN
activities a
ON
a.id = p.activity
LEFT JOIN
responsible_persons rp
ON
rp.ProjectID = p.ProjectID AND rp.UserID = p_currentUserId
LEFT JOIN
users u
ON
u.UserID = p_currentUserId
WHERE
(u.User_roleID = 1 AND
p.CustomName LIKE CONCAT((SELECT CustomName FROM projects pr WHERE pr.ProjectID = p_projectId), '%') AND p.ProjectID <> p_projectId)
OR
((
(p.Responsible_person_id = p_currentUserId OR p.Delivery_contact = p_currentUserId OR rp.UserID = p_currentUserId OR (pusd.UserID = p_currentUserId AND SYSTIMESTAMP BETWEEN TO_DATE(pusd.StartDate,'YYYY-MM-DD') AND TO_DATE(pusd.EndDate,'YYYY-MM-DD') + INTERVAL '1' DAY AND
SYSTIMESTAMP BETWEEN TO_DATE(p.StartDate,'YYYY-MM-DD') AND TO_DATE(p.EndDate,'YYYY-MM-DD') + INTERVAL '1' DAY))
)
AND
p.CustomName LIKE CONCAT((SELECT CustomName FROM projects pr WHERE pr.ProjectID = p_projectId), '%') AND p.ProjectID <> p_projectId)
ORDER BY p.CustomName;
RETURN rc;
END GET_SUB_PROJECTS;
When I call function it needs to return data, but it doesn't. Somehow, here p.Responsible_person_id and p.Delivery_contact needs to be NUMBER but somehow it is VARCHAR
When I call function I use
SELECT PROJECT_PACKAGE.GET_SUB_PROJECTS('199',141) FROM DUAL
I found one solution to modify but It throw me error like
Error report -
ORA-01439: column to be modified must be empty to change datatype
01439. 00000 - "column to be modified must be empty to change datatype"
What to do in this situation ? What is the best method to solve this issue ?

Answer 1

You can change the data type of a column online using dbms_redefinition
create table t (
c1 varchar2(10)
primary key
);
create table t_new (
c1 number(10, 0)
primary key
);
insert into t values ( '1.0000' );
commit;
begin
dbms_redefinition.start_redef_table (
user, 't', 't_new',
col_mapping => 'to_number ( c1 ) c1',
options_flag => dbms_redefinition.cons_use_rowid
);
end;
/
exec dbms_redefinition.sync_interim_table ( user, 't', 't_new' );
exec dbms_redefinition.finish_redef_table ( user, 't', 't_new' );
desc t
Name Null? Type
C1 NOT NULL NUMBER(10)
select * from t;
C1
1
There are also options to copy constraints, triggers, indexes, etc. automatically in this process.