SQL Query returning no rows, please help!!

Question

I have a table that contains user audits for a particular procedures alongwith the date stamp. Now, I want to list all the procedures not accessed by the users within the last 6 months. Or, all the procedures that have not been used/accessed during the last 6 months.
This is what I am trying but is not returning any rows:
SELECT DISTINCT proc_name,
TRUNC (entry_date)
FROM log_web
WHERE proc_name NOT IN (SELECT proc_name
FROM log_web
WHERE TRUNC (entry_date) > TRUNC (SYSDATE - 180))
ORDER BY 2 DESC
Please advise.
Thank you in advance.

Answer 1

Two possibilities leap to mind.
First, are you sure that there are any prodcedures not accessed in the last six months?
Second, is there a chance that there could be records with a null value in proc_name? If the sub-query used in a NOT IN predicate returns even one null value, the query will return no rows.
Does this return rows?
SELECT DISTINCT proc_name, TRUNC(entry_date)
FROM log_web
WHERE proc_name NOT IN (SELECT proc_name
                        FROM log_web
                        WHERE TRUNC (entry_date) > TRUNC (SYSDATE - 180) and
                              proc_name IS NOT NULL)
ORDER BY 2 DESCJohn