Query to run select statement conditionally

Question

Want: when either variable is null then run a full report, if both variables are not null then run the report with range specified
I have the following query, but kept getting invliad sql error. Can you help ?
IF (:P1_START_DATE IS NULL or :P1_END_DATE IS NULL)
THEN select empno,ename,job,mgr, hiredate from emp;
else IF (:P1_START_DATE IS NOT NULL and :P1_END_DATE IS NOT NULL)
then select empno,ename,job,mgr, hiredate from emp where hiredate between :P1_START_DATE and :P1_END_DATE;
end if;
Tai

Answer 1

Hi,
The way most people deal with that problem is to always filter on parameters, but, when a parameter is not passed, make it default to some value that wuill include all rows. With DATEs, that's easy, because it's easy to specify the earliest and latest DATEs that are possible in Oracle:
Assuming the datatype of :p1_start_date and :p1_end_date is DATE:
SELECT  empno
,     ename
,     job
,     mgr
,     hiredate
FROM    emp
WHERE   hiredate     BETWEEN NVL ( :P1_START_DATE
                                  , T0_DATE ('1', 'J')
                         AND     NVL ( :P1_END_DATE
                        , TO_DATE ('31-Dec-9999')
;Te query above treats each parameter independently. If, say, :p1_start_date is NULL, but :p1_end_date is, say, January 1, 2005, then the query above would look for people hired on before January 1, 2005. That is, there would not be a lower limit to hiredate, because :p1_start_date was NULL, but there would be an upper limit, because :p1_end_date was not NULL.
You're saying that if either parameter is NULL, you want to ignore both of them, not just the one that is NULL.
Here's one way to do that:
SELECT  empno
,     ename
,     job
,     mgr
,     hiredate
FROM    emp
WHERE   hiredate     BETWEEN NVL ( LEAST ( :P1_START_DATE
                                   , :P1_END_DATE
                                  , T0_DATE ('1', 'J')
                         AND     NVL ( GREATEST ( :P1_START_DATE
                                      , :P1_END_DATE
                        , TO_DATE ('31-Dec-9999')
;This will also automatically correct the error if someone enters the parameters in the wrong order.
If you're doing this in PL/SQL, and speed is very impratant, then you may want to have tow separate queries (one with a WHERE clause, the other without), as in the example you posted.
Edited by: Frank Kulash on Jun 18, 2010 3:29 PM
MScallion's solution is better.
It can be simplified like this:
WHERE  :p1_start_date     IS NULL
OR     :p1_end_date     IS NULL
OR     hiredate          BETWEEN :p1_start_date
                      AND     :p1_end_date