How to fetch into collection using ref cursor, when the record count in table is a multiple of the limit number specified? - sql

Question

create table with id column
CREATE TABLE TEST_TAB
(ID NUMBER
);
create type
CREATE type numbertabletype IS TABLE OF NUMBER;
insert 100 records
INSERT INTO TEST_TAB
SELECT LL FROM
(SELECT LEVEL LL FROM DUAL CONNECT BY LEVEL<=100
);
Create function that loops through 100 records in 10 loops, cursor will fetch into numbertable type collection with LIMIT 10.
CREATE OR REPLACE FUNCTION LOOP_TEST
RETURN NUMBERTABLETYPE
IS
lv_coll NUMBERTABLETYPE ;
LV_COUNT NUMBER:=0;
CURSOR c1
IS
SELECT ID FROM TEST_TAB WHERE ROWNUM<=100;
BEGIN
OPEN c1;
LOOP
dbms_output.put_line('BEFORE FETCH CURSOR COUNT '||C1%ROWCOUNT);
FETCH c1 bulk collect INTO lv_coll limit 10;
dbms_output.put_line('AFTER FETCH CURSOR COUNT '||C1%ROWCOUNT);
EXIT
WHEN c1%NOTFOUND;
LV_COUNT:=LV_COUNT+1;
dbms_output.put_line(' BELOW NOT FOUND '||LV_COUNT);
dbms_output.put_line('COLLECTION COUNT '||lv_coll.count);
END LOOP;
CLOSE c1;
RETURN lv_coll;
END;
/
Run sql as script, it returns null when rownum = 100
CURSOR c1
IS
SELECT ID FROM TEST_TAB WHERE ROWNUM<=100;
Run sql as script, it returns values when rownum = 99, replace cursor c1 in function with below cursor.
CURSOR c1
IS
SELECT ID FROM TEST_TAB WHERE ROWNUM<=99;
so How do you tackle a scenario when the limit is a multiple of total records to loop.

Answer 1

The code is working perfectly; it is just not doing what you expect.
When the code loops it will overwrite the lv_coll collection each time so that it will contain no more than 10 items.
When it fetches the 91-100th rows it fills the collection with 10 items and processes it but, because it has not tried to read another row, it is unaware that there are no more rows left in the cursor and has not yet reached the c1%NOTFOUND condition to terminate the loop.
When it repeats the loop, after that, it will find that the cursor has now been exhausted and will read zero rows. So, in this final loop, the lv_coll collection is not NULL but is a collection containing zero elements and that is what is going to get returned.
Compare this to when there are only 99 rows in the cursor. When the loop tries to read the 91st - 100th rows it will read the 91st - 99th rows and try to read the 100th but will find that the cursor has been exhausted and c1%NOTFOUND will be true exiting the loop and causing the collection to be returned with only 9 items.
If you want to return all the elements from the cursor then you will need to use a second collection to aggregate them as the one populated from the cursor will be overwritten at each loop:
CREATE OR REPLACE FUNCTION LOOP_TEST
RETURN NUMBERTABLETYPE
IS
lv_coll NUMBERTABLETYPE;
all_items NUMBERTABLETYPE := NUMBERTABLETYPE();
LV_COUNT NUMBER:=0;
ids VARCHAR2(30);
CURSOR c1
IS
SELECT ID FROM TEST_TAB WHERE ROWNUM<=100;
BEGIN
OPEN c1;
LOOP
dbms_output.put_line('BEFORE FETCH CURSOR COUNT '||C1%ROWCOUNT);
FETCH c1 bulk collect INTO lv_coll limit 10;
dbms_output.put_line('AFTER FETCH CURSOR COUNT '||C1%ROWCOUNT);
EXIT WHEN c1%NOTFOUND;
LV_COUNT:=LV_COUNT+1;
all_items := all_items MULTISET UNION ALL lv_coll;
dbms_output.put_line(' BELOW NOT FOUND '||LV_COUNT);
dbms_output.put_line('COLLECTION COUNT '||lv_coll.count);
-- SELECT LISTAGG(COLUMN_VALUE,',') WITHIN GROUP( ORDER BY ROWNUM )
-- INTO ids
-- FROM TABLE(lv_coll);
-- dbms_output.put_line('IDS: '||ids);
END LOOP;
CLOSE c1;
RETURN all_items;
END;
/
Which can be called using:
DECLARE
ids numbertabletype;
vals VARCHAR2(3000);
BEGIN
ids := LOOP_TEST();
DBMS_OUTPUT.PUT_LINE( 'NUMBER OF IDs: ' || CASE WHEN ids IS NULL THEN 'NULL' ELSE TO_CHAR( ids.COUNT ) END );
SELECT LISTAGG(COLUMN_VALUE,',') WITHIN GROUP( ORDER BY ROWNUM )
INTO vals
FROM TABLE(ids);
DBMS_OUTPUT.PUT_LINE( 'values: ' || vals );
END;
/
db<>fiddle here

Answer 2

I tried to run your case in an anonymous block and it failed to output in case of ROWNUM<=100.
I changed the little bit in your code and it worked.
--
DECLARE
lv_coll NUMBERTABLETYPE ;
lv_col2 NUMBERTABLETYPE ; -- added this line to hold the data
LV_COUNT NUMBER:=0;
CURSOR c1
IS
SELECT ID FROM TEST_TAB WHERE ROWNUM<=100;
BEGIN
OPEN c1;
LOOP
--dbms_output.put_line('BEFORE FETCH CURSOR COUNT '||C1%ROWCOUNT);
FETCH c1 bulk collect INTO lv_coll limit 10;
EXIT WHEN lv_coll.COUNT = 0; -- added this line
lv_col2 := lv_coll; -- added this line
--dbms_output.put_line('AFTER FETCH CURSOR COUNT '||C1%ROWCOUNT);
-- EXIT
--WHEN c1%NOTFOUND;
-- LV_COUNT:=LV_COUNT+1;
--dbms_output.put_line(' BELOW NOT FOUND '||LV_COUNT);
--dbms_output.put_line('COLLECTION COUNT '||lv_coll.count);
END LOOP;
CLOSE c1;
--RETURN lv_coll;
FOR I IN 1..lv_col2.COUNT LOOP -- added this line
dbms_output.put_line(lv_col2(I)); -- added this line
END LOOP;
END;
/
db<>fiddle demo