ORA-01002: fetch out of sequence in procedure - oracle

Question

I created a procedure in oracle database that returns data in a ref-cursor, and I want it to return the rowcount of this cursor also as an output variable. After testing, the P_count variable is filled correctly, but when I tried to open it an
ORA-01002: fetch out of sequence
error is fired. I have read before about it and I found that the problem is because I am using a fetch statement in. But till now I did not discover how to resolve it. Any helps are appreciated, thank you.
Below is my Procedure:
PROCEDURE IS_CLIENT_LOGGED_IN (P_CLIENT_NUM Varchar2,P_CURSOR out SYS_REFCURSOR ,P_COUNT OUT NUMBER,P_ERROR out Varchar2) AS
TYPE MyRec IS RECORD (ID VARCHAR2(100));
cur_rec MyRec;
lv_cur SYS_REFCURSOR;
BEGIN
BEGIN
Open lv_cur FOR
SELECT ID
FROM tbl_registration
WHERE tbl_client_id = P_CLIENT_NUM
AND tbl_logout_date is null;
LOOP
FETCH lv_cur INTO cur_rec;
EXIT WHEN P_CURSOR%notfound;
P_COUNT := P_CURSOR%rowcount;--will return row number beginning with 1
END LOOP;
P_CURSOR := lv_cur;
EXCEPTION WHEN OTHERS THEN
P_ERROR := 'Unable to select Data from tbl_registration' ||SQLERRM;
END;
Searching online I found reasons for the issue as below:
Fetching from a cursor after the last row has been retrieved and the ORA-1403 error returned.
If the cursor has been opened with the FOR UPDATE clause, fetching after a COMMIT has been issued will return the error.
Rebinding any placeholders in the SQL statement, then issuing a fetch before reexecuting the statement.
But I cannot find a proper solution.

Answer 1

You can only use a cursor once, so if you want both the row count and the actual result set, you will need two separate queries. Then the problem is that the data might have been updated by other sessions between the two queries, giving inconsistent results. (For example, another session inserted some rows earlier, and then commits while your procedure is running.)
One approach would be to use flashback query to ensure that the count and the fetch refer to the same point in time:
create or replace procedure is_client_logged_in
( p_client_num varchar2
, p_cursor out sys_refcursor
, p_count out number
, p_error out varchar2 )
as
k_starttime constant timestamp := systimestamp;
begin
select count(*) into p_count
from tbl_registration as of timestamp k_starttime
where tbl_client_id = p_client_num
and tbl_logout_date is null;
open p_cursor for
select id
from tbl_registration as of timestamp k_starttime
where tbl_client_id = p_client_num
and tbl_logout_date is null;
exception
when others then p_error := 'Unable to retrieve registration data.'||chr(10)||sqlerrm;
end;

Answer 2

What you want sounds very simple, but isn't. A cursor is for one-use only. So if you read through it, you are done with it. Returning the unused cursor plus its row count requires special handling hence.
One way to come to mind is two separate queries: One to count the rows, one to open the cursor. The problem, though: In the nanoseconds between the queries the row count may change because of other sessions inserting or deleting or updating data. Okay, you can lock the table exclusively, but then you will have to release it after the two statements. Unfortunately, there is no UNLOCK TABLE command in Oracle. Releasing a table is only possible via a COMMIT or ROLLBACK. So, in order not to interfere with the caller's transaction you need a SAFEPOINT, too.
Here is your procedure with the above method applied:
CREATE OR REPLACE PROCEDURE is_client_logged_in (p_client_num VARCHAR2, p_cursor OUT SYS_REFCURSOR, p_count OUT NUMBER, p_error OUT VARCHAR2) AS
BEGIN
SAVEPOINT for_unlock;
LOCK TABLE tbl_registration IN EXCLUSIVE MODE;
SELECT COUNT(*) INTO p_count
FROM tbl_registration
WHERE tbl_client_id = p_client_num
AND tbl_logout_date IS NULL;
Open p_cursor FOR
SELECT id
FROM tbl_registration
WHERE tbl_client_id = p_client_num
AND tbl_logout_date IS NULL;
ROLLBACK TO SAVEPOINT for_unlock;
EXCEPTION WHEN OTHERS THEN
ROLLBACK TO SAVEPOINT for_unlock;
p_error := 'Unable to select Data from tbl_registration' || SQLERRM;
END is_client_logged_in;
Demo: https://dbfiddle.uk/?rdbms=oracle_18&fiddle=552d7f76d03a9a221c17f05c6663d2c9

Answer 3

Here is an alternative. It's really muddling through, but well...
I've shown a solution with locking the table. But imagine a query that runs for an hour. You'd lock that table for twice this time.
William has shown a great solution with flashback queries. But with a query running for an hour, the flashback data may time out.
So, here is a weird solution getting count and results in one query. This is easy in your case, because I expect the ID you are selcting to be an integer, just as the count. So I select the count into the first row, fetch that and give back the cursor that is now at the position for the first actual data row (the first ID).
CREATE OR REPLACE PROCEDURE is_client_logged_in (p_client_num VARCHAR2, p_cursor OUT SYS_REFCURSOR, p_count OUT NUMBER, p_error OUT VARCHAR2) AS
BEGIN
Open p_cursor FOR
WITH data AS
(
SELECT id
FROM tbl_registration
WHERE tbl_client_id = p_client_num
AND tbl_logout_date IS NULL
)
SELECT id
FROM
(
SELECT 1 as sortkey, COUNT(*) AS id FROM data
UNION ALL
SELECT 1 as sortkey, id FROM data
)
ORDER BY sortkey;
FETCH p_cursor INTO p_count;
EXCEPTION WHEN OTHERS THEN
p_error := 'Unable to select Data from tbl_registration' || SQLERRM;
END is_client_logged_in;
Demo: https://dbfiddle.uk/?rdbms=oracle_18&fiddle=24ed333b9c1ed700af6d3a486ef47ccd