Check if Exists PLS-00405: subquery not allowed in this context - oracle

Question

I have cursor it selects from TableA then Fetch Loop that inserts into TableB.
I want to check if the value already exists in the TableB.
If it exists then I want to skip the insert.
create or replace
PROCEDURE DAILY_RPT (
v_start IN DATE,
v_end IN DATE)
IS
ao_out_no out_pair.out_no%type;
cursor get is
SELECT ao_out_no from tableA;
BEGIN
open get;
LOOP
fetch get into ao_out_no;
EXIT WHEN get%NOTFOUND;
if (ao_out_no = (select out_no from TableA where out_no = ao_out_no) THEN
--DO NOTHING
else
INSERT INTO TABLEB(OUT_NO) VALUES (ao_out_no);
end if;
END LOOP;
close get;
END;
I used IF CONDITION however, I used variable into if condition & I am getting below.
PLS-00405: subquery not allowed in this context
if (ao_out_no = (select out_no from TableA where out_no = ao_out_no) THEN

Answer 1

You don't need cursor or PL/SQL at all:
INSERT INTO TABLEB(OUT_NO)
SELECT ao_out_no
FROM tableA ta
WHERE ... -- filtering rows
AND NOT EXISTS (SELECT * From TableB tb WHERE tb.OUT_NO = ta.ao_out_no);

Answer 2

Use the following :
for i in (
select out_no from TableA where out_no
)
loop
if i.out_no = ao_out_no
then
-- DO NOTHING
else
...
or
create a new variable named x, and then assign a value to it by
select out_no into x from TableA where out_no = ao_out_no;
and check returning value for x.

Answer 3

With corrected syntax, it would be something like this:
create or replace procedure daily_rpt
( v_start in date
, v_end in date )
as
begin
for r in (
select ao_out_no, 0 as exists_check
from tablea
)
loop
select count(*) into exists_check
from tablea
where out_no = r.ao_out_no
and rownum = 1;
if r.exists_check > 0 then
--DO NOTHING
else
insert into tableb (out_no) values (r.ao_out_no);
end if;
end loop;
end;
However, it's inefficient to query all of the rows and then do an additional lookup for each row to decide whether you want to use it, as SQL can do that kind of thing for you. So version 2 might be something like:
create or replace procedure daily_rpt
( v_start in date
, v_end in date )
as
begin
for r in (
select ao_out_no
from tablea
where not exists
( select count(*)
from tablea
where out_no = r.ao_out_no
and rownum = 1 )
)
loop
insert into tableb (out_no) values (r.ao_out_no);
end loop;
end;
at which point you might replace the whole loop with an insert ... where not exists (...) statement.