Can't get query to work. table alias in subquery in FROM clause

Question

How can I rearrange this query to work?
SELECT
                           TO_CHAR(dt.date_time, 'YYYY-MM-DD') start_date,
                                   (SELECT COUNT(*) FROM
                                        (SELECT DISTINCT a.non_asp, a.start_time, a.end_time
                                              FROM appointments a
                  WHERE  a.start_time >= dt.date_time AND a.start_time < dt.date_time + 1
                                   ) num_overlap
                         FROM
                              table(times_pkg.between_times(TO_DATE('2010-05-30'),
                                         TO_DATE('2010-07-03'), 60*24, 'Y')) dtbetween_times is a table function that returns times at given intervals.
I am trying to get a count of distinct (non_asp, start_time, end_time) sets that fall on each day.
However, it doesn't recognize dt.date_time in the FROM clause.

Answer 1

Hi,
A sub-query can be correlated only to its immediate parent. You're trying the correlate the SELECT DISTINCT sub-query to its grandparent.
You can re-write the sub-query as a join, like this:
SELECT  TO_CHAR(dt.date_time, 'YYYY-MM-DD') start_date,
     a.num_overlap
FROM     table ( times_pkg.between_times ( TO_DATE('2010-05-30'),
                           TO_DATE('2010-07-03'),
                           60*24,
                           'Y'
           ) dt
JOIN    (
       SELECT    start_time,
                end_time,
              COUNT (DISTINCT non_asp)     AS num_overlap
       FROM         appointments
     )  a         ON  a.start_time         >= dt.date_time
              AND a.start_time         < dt.date_time + 1
;You could also eliminate the extra level between the SELECT DISTINCT sub-query and the main query by using SELECT (DISTINCT ...).