Functions: Passing Parameters

Question

Hi,
I have created a function to return a number. I am passing the following items:
person_id NUMBER
start_date DATE
end_date DATE
Function Condition:
WHERE person_id = person_id_in
AND start_date between START_DATE_IN and END_DATE_IN
I am calling the function in a sql statement:
select person_id, HC_GET_BFACTOR(p.person_id, '01-apr-2004', '30-apr-2004') as "Bradford Factor",
from employees
where start_date BETWEEN '01-apr-2004' AND '30-apr-2004'
This works fine, but is there a way to avoid entering the dates in the function ( ) as hardcoded above. The between clause will be used as a parameter for users to enter the start_date and end_date but how can these values be passed in the parameter without hardcoding them HC_GET_BFACTOR(p.person_id, '01-apr-2004', '30-apr-2004')
p.s i will be using this function in OBIEE, the start_date and end_date will be parameter prompts for the user to enter the dates. I would like the function to pick these parameter dates.
Can anyone help?
Thanks

Answer 1

Hi,
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If the 2nd ard 3rd arguments to your function are DATEs, then don't pass strings.    Pass DATEs instead.
If start_date is a column in your table, don't compare it to string.  Compare it to DATEs instead.
The arguments to the function amd the conditions in your WHERE clause are completely independent.  I don't know of any way to specify the value once and have it apply both to the function and to the WHERE clause.
You could avoid having a function at all, which would probably be faster.
Start your query with a WITH clause that narrows down the result as much as possible, including filtering by the date parameters.  Base the rest of the query, including a sub-query like the one in your function, on that filtered result set.
The probelm with that approach is that you have to do a similar sub-query in every statement where you might want to use the function.  If you really want the convenience of a function, that won't work.
You can specify the parameters in just one place, and use the values in multiple places.
For example:WITH     params          AS
     SELECT     TO_DATE ( '01-apr-2004'
               , 'DD-MON-YYYY'
               )     AS min_start_date
     ,     TO_DATE ( '30-apr-2004'
               , 'DD-MON-YYYY'
               )     AS max_start_date
     FROM     dual
SELECT     person_id
,     hc_get_bfactor (person_id, min_start_date, max_start_date)
FROM     employees
CROSS JOIN params
WHERE     start_date BETWEEN min_start_date
          AND     max_start_date
If you want to change the cutoff date to, say, April 10 instead of April 30, then you just have to make the change in one place.
Instead of using a sub-query (like params, above), you could create a global temporary table to hold the parameters, or store them in SYS_CONTEXT variables.  Either way, multiple sessions could run the same statements at the same time, each with their own parameter values.  The function wouldn't need the DATE parameters; it would read the values from the global temporary table or call SYS_CONTEXT to get the values. Or you might make the DATE arguments optional, and get the values from the table or SYS_CONTEXT only when they were not passed.