Search for value otherwise select all...decode?

Question

Hi all,
I'm wanting a reasonably straight forward (sounding) result from a query: I want to select data where a certain column equals a value, otherwise I want to return all results.
Let me know if you need more details.
Thanks!

Answer 1

Hi,
djston wrote:
Hi all,
I'm wanting a reasonably straight forward (sounding) result from a query: I want to select data where a certain column equals a value, otherwise I want to return all results.
Let me know if you need more details.Whenever you have a problem, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only). You can skip this if the problem is based on commonly available tables, like those in the scott schema.
Also post the results you want from that data, and an explanation of how you get those results from that data, with specific examples.
If the problem involves parameters, give a couple of examples of different parameters, and the results you want from each.
Always say which version of Oracle you're using.
For example:
"I'm using Oracle 10.2.0.3.0.
I want to find all the people in the scott.emp table who have a given job; but if nobody has that job, then I want to select everybody.
For example, if I give 'MANAGER' as the parameter, then I want these results:
{code}
ENAME JOB
BLAKE MANAGER
CLARK MANAGER
JONES MANAGER
{code}
because those are the only people in the table with job='MANAGER'.
However, if I give 'DBA' as the parameter, then I want to see all 14 rows from the table, because there is no row where job='DBA'."
If that happens to be what you want, here's one way to do it:
VARIABLE     target_job     VARCHAR2 (10)
-- EXEC     :target_job := 'DBA';
-- EXEC     :target_job := 'PRESIDENT';
EXEC     :target_job := 'MANAGER';
SELECT       ename, job
FROM       scott.emp
WHERE       job          = :target_job
OR       NOT EXISTS     (
                       SELECT  1
                   FROM    scott.emp
                   WHERE   job     = :target_job
ORDER BY  ename
;Noticed that this query involves an extremely rare un-correlated EXISTS sub-query. (At least intentionally un-correlated EXISTS sub-queries are rare.)
You could get the same results using DENSE_RANK and a CASE expression.