Using case on return value of subquery - sql

Question

I'd like to write case clause which takes its input from inner query. Please let me describe this in more detail.
Say I have a table:
create table food
( fruit varchar2(50),
chips varchar2(50)
);
with values
INSERT INTO food
(fruit, chips)
VALUES ('Apple', 'Paprika');
INSERT INTO food
(fruit, chips)
VALUES ('Orange', 'Salt');
DB Fiddle
I would like to write a query that will show:
fruit, chips and 1 if fruit is 'Apple' and 0 otherwise
which would give a result (example)
'Apple', 'Paprika', 1
'Orange, 'Salt', 0
I do not want use joins for this. It has to be subquery. That's a requirement I must comply with.
I've come up with the following query:
select f.fruit,
((case (select ff.fruit from food ff)
when ff.fruit = 'Apple' then 1 else 0 end ) as is_apple) from food f;
However, I get the following error ORA-00905: missing keyword

Answer 1

You don't need a subquery for this:
select fruit, chips,
case when fruit = 'Apple'
then 1
else 0
end as is_apple
from food
If the value must be the result of a subquery, you may use:
select fruit, chips,
(select case when f2.fruit = 'Apple'
then 1
else 0
end
from food f2
where f.rowid = f2.rowid
)
from food f

Answer 2

If it has to be subquery then use dual:
select fruit, chips,
(select case food.fruit when 'Apple' then 1 else 0 end from dual) is_apple
from food;
or subselect from food using primary key (if your table contains it), or rowid:
select fruit, chips,
case (select fruit from food ff where ff.rowid = food.rowid)
when 'Apple' then 1
else 0
end is_apple
from food;
demo