Cursor error in SQL - sql

Question

I'm trying to implement a cursor, & after solving many errors I've finally come to a point where it runs, but it goes into infinite loop...
I've put the image of table below as image.
Aim of cursor: to calculate bowling average & store in 'bowling_avg' column.
here's the cursor code :
DECLARE
CURSOR BOWL_AVG IS SELECT SID,MATCHES,BOWLING_AVG,WICKETS
FROM BOWLING_STATS ;
NSID BOWLING_STATS.SID%TYPE;
NMATCHES BOWLING_STATS.MATCHES%TYPE;
NBOWLING_AVG BOWLING_STATS.BOWLING_AVG%TYPE;
NWICKETS BOWLING_STATS.WICKETS%TYPE;
BEGIN
OPEN BOWL_AVG;
IF BOWL_AVG%ISOPEN THEN
LOOP
FETCH BOWL_AVG INTO NSID,NMATCHES,NBOWLING_AVG,NWICKETS;
EXIT WHEN BOWL_AVG%NOTFOUND;
IF BOWL_AVG%FOUND THEN
LOOP
UPDATE BOWLING_STATS SET BOWLING_AVG=NWICKETS/NMATCHES WHERE SID=NSID ;
EXIT WHEN BOWL_AVG%NOTFOUND;
END LOOP;
END IF;
END LOOP;
ELSE
DBMS_OUTPUT.PUT_LINE('UNABLE TO OPEN CURSOR');
END IF;
CLOSE BOWL_AVG;
END;
I'm running this in oracle database 10g.
I ask for assistance in finding the error.
Thanks in advance.

Answer 1

Adding whitespace to your code makes it clearer what you're doing:
declare
cursor bowl_avg is
select sid, matches, bowling_avg, wickets
from bowling_stats;
nsid bowling_stats.sid%type;
nmatches bowling_stats.matches%type;
nbowling_avg bowling_stats.bowling_avg%type;
nwickets bowling_stats.wickets%type;
begin
-- 1. Open Cursor
open bowl_avg;
-- 2. Check if Cursor is open
if bowl_avg%isopen then
-- 3. Loop
loop
-- 4. Get record
fetch bowl_avg into nsid, nmatches, nbowling_avg, nwickets;
-- 5. Exit if no records left
exit when bowl_avg%notfound;
-- 6. If there is a record
if bowl_avg%found then
-- 7. Loop
loop
update bowling_stats
set bowling_avg = nwickets / nmatches
where sid = nsid;
-- 8. Exit if there is no record.
exit when bowl_avg%notfound;
end loop;
end if;
end loop;
else
dbms_output.put_line('unable to open cursor');
end if;
close bowl_avg;
end;
/
There are a number of contradictions in there.
In 1 and 2 you're opening a cursor and then checking if there is an open cursor. A error will be raised if the cursor didn't open so you can ignore this step.
In 5 and 6 you exit if you can't fetch a new record then check if you have a record. This is a contradiction so stage 6 will (almost) always evaluate to true.
in 7 and 8 you loop, exiting when you don't have a record. As you've just checked (twice) that you do in fact have a record you'll never exit this loop.
If you insist on doing this with cursors then you can remove most of your code and it should work fine:
declare
cursor bowl_avg is
select sid, matches, bowling_avg, wickets
from bowling_stats;
nsid bowling_stats.sid%type;
nmatches bowling_stats.matches%type;
nbowling_avg bowling_stats.bowling_avg%type;
nwickets bowling_stats.wickets%type;
begin
-- 1. Open Cursor
open bowl_avg;
-- 2. Loop
loop
-- 3. Get record
fetch bowl_avg into nsid, nmatches, nbowling_avg, nwickets;
-- 4. Exit loop if there is no record.
exit when bowl_avg%notfound;
-- 5. Perform UPDATE statement.
update bowling_stats
set bowling_avg = nwickets / nmatches
where sid = nsid;
end loop;
close bowl_avg;
end;
/
As always a single UPDATE statement without using loops, cursors or PL/SQL will be significantly more effective.