If table have 0 rows exit procedure - sql

Question

I have a procedure inside a package and I want to implement a logic, wich will not insert the temp table into the main table if the temp table have 0 rows, and then go to the next procedure of the package.
IF (not exists(select 1 from temp)) THEN
RETURN;
ELSE
EXECUTE IMMEDIATE 'TRUNCATE TABLE main';
INSERT --+APPEND
INTO main
Select * from temp;
EXECUTE IMMEDIATE 'TRUNCATE TABLE temp';
END IF;
With this solution, the package is compiled with error.
Can anyone give me some tips?

Answer 1

you can use loop, without any variables, just first iteration, something like this
FOR a in (select 1 from temp where rownum = 1) LOOP
EXECUTE IMMEDIATE 'TRUNCATE TABLE main';
INSERT --+APPEND
INTO main
Select * from temp;
EXECUTE IMMEDIATE 'TRUNCATE TABLE temp';
END LOOP;

Answer 2

Just count one row and then test whether the result is 0 or 1:
declare
l_row_check integer := 0;
begin
select count(*) into l_row_check from main
where rownum = 1;
if l_row_check = 0 then
execute immediate 'truncate table main';
insert --+ append
into main
select * from temp;
execute immediate 'truncate table temp';
end if;
end;

Answer 3

The easiest is to use a variable to check:
--- suggested edit: add condition to select 1 row at most and avoid
-- counting big table.
select count(1) into v_count from temp where rownum <=1;
IF (v_count=0) THEN
RETURN;
ELSE
EXECUTE IMMEDIATE 'TRUNCATE TABLE main';
INSERT --+APPEND
INTO main
Select * from temp;
EXECUTE IMMEDIATE 'TRUNCATE TABLE temp';
END IF;

Answer 4

Some answer on here use a SELECT INTO method, but I find those a bit tricky.
Since if for example SELECT ColumnA INTO vcColumnA FROM Temp will not have any records, you will end up with the error ORA-01403: no data found.
And those can be hard to find if you have a bigger database.
To loop through a table and do something with values I think cursors and records are more safe.
For example:
DECLARE
CURSOR cTemp IS
SELECT ColumnA, ColumnB
FROM Temp;
rTemp cTemp%ROWTYPE;
BEGIN
OPEN cTemp;
LOOP
FETCH cTemp INTO rTemp;
-- Exit when we read all lines in the Temp table.
EXIT WHEN cTemp%NOTFOUND;
--Do something with every row.
--For example, print ColumnB.
DBMS_OUTPUT.PUT_LINE(rTemp.ColumnB);
END LOOP;
CLOSE cTemp;
END;
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