How to check existence in Oracle without scanning the entire table?

Question

Normally, to check existence in Oracle I will do:

SELECT COUNT(1)
FROM foo
WHERE bar = 'baz'

However, if the foo table contains multiple rows where bar='baz', this query needlessly scans through the entire table in order to report the total count.

How do I quickly check if a column in a table contains at least one row with a specified value, and have the query short-circuit, such that as soon as it detects that the value exists, the query will stop and return, as opposed to scanning the entire table?

Ideally I would want this query to return a scalar value, regardless of how many rows in the table contain the value.

---

The following solution appears to short-circuit (compared to SELECT COUNT(1), this is much faster for a large table), however it will either return 1 if the value exists, or return no rows at all if the value does not exist. It would be better if a row was always returned.

SELECT 1
FROM DUAL
WHERE EXISTS (
    SELECT 1
    FROM foo
    WHERE bar = 'baz'
)

Answer 1

Just combine the two:

SELECT count(*)
FROM DUAL
WHERE EXISTS (
    SELECT 1
    FROM foo
    WHERE bar = 'baz'
)

Answer 2

Beside Balazs' natural improvement of your query the following should work

select count(*)
from foo
where bar='baz'
and rownum=1