[8i] Help with function with parameters (for workday calculation)

Question

Let me start by saying, I've never written a function before, and I don't have access to create a function in my database (i.e. I can't test this function). I'm trying to come up with a function that I can ask my IT department to add for me. I'm hoping someone can take a look at what I've written and tell me if it should work or not, and if this is the right way to go about solving my problem.
I am trying to create a function to do a very simple workday calculation (adding/subtracting a particular number of workdays from a calendar date).
The database I'm working with has a table with the workday calendar in it. Here is a sample table and sample data, representative of what's in my workday calendar table:
CREATE TABLE caln
(     clndr_dt     DATE,
     shop_days     NUMBER(5)
     CONSTRAINT caln_pk PRIMARY KEY (clndr_dt)
INSERT INTO     caln
VALUES (To_Date('01/01/1980','mm/dd/yyyy'),0);
INSERT INTO     caln
VALUES (To_Date('01/02/1980','mm/dd/yyyy'),1);
INSERT INTO     caln
VALUES (To_Date('01/03/1980','mm/dd/yyyy'),2);
INSERT INTO     caln
VALUES (To_Date('01/04/1980','mm/dd/yyyy'),3);
INSERT INTO     caln
VALUES (To_Date('01/05/1980','mm/dd/yyyy'),3);
INSERT INTO     caln
VALUES (To_Date('01/06/1980','mm/dd/yyyy'),3);
INSERT INTO     caln
VALUES (To_Date('01/07/1980','mm/dd/yyyy'),4);
INSERT INTO     caln
VALUES (To_Date('01/08/1980','mm/dd/yyyy'),5);
INSERT INTO     caln
VALUES (To_Date('01/09/1980','mm/dd/yyyy'),6);
INSERT INTO     caln
VALUES (To_Date('01/10/1980','mm/dd/yyyy'),7);
INSERT INTO     caln
VALUES (To_Date('01/11/1980','mm/dd/yyyy'),8);
INSERT INTO     caln
VALUES (To_Date('01/12/1980','mm/dd/yyyy'),8);
INSERT INTO     caln
VALUES (To_Date('01/13/1980','mm/dd/yyyy'),8);
INSERT INTO     caln
VALUES (To_Date('01/14/1980','mm/dd/yyyy'),9);The actual table includes from 1/1/1980 though 12/31/2015.
I've written (and validated) this parameter query which does my workday (mday) calculation:
SELECT     cal.clndr_dt
FROM     CALN cal
     SELECT     cal.shop_days+:mdays     AS new_shop_days
     FROM     CALN cal
     WHERE     cal.clndr_dt     =:start_date
     ) a
WHERE     cal.shop_days     = a.new_shop_days
AND     ROWNUM          =1
ORDER BY     cal.clndr_dt;Based on this query, I've created the following function (and I have no clue if it works or if the syntax is right, etc.):
CREATE OR REPLACE FUNCTION add_mdays
     (start_date     IN DATE,
     mdays          IN NUMBER(5))
RETURN     DATE
IS
     new_date DATE;
BEGIN
     SELECT     cal.clndr_dt
     FROM     CALN cal
          SELECT     cal.shop_days+mdays     AS new_shop_days
          FROM     CALN cal
          WHERE     cal.clndr_dt     =start_date
          ) a
     WHERE     cal.shop_days     = a.new_shop_days
     AND     ROWNUM          =1
     ORDER BY     cal.clndr_dt;
     RETURN     new_date;
END add_mdays;  //edit 9:31 AM - noticed I left off this bitI'm also not sure how to have the function handle results that would return a date outside of the date range that is in the table (Before 1/1/1980 or after 12/31/2015--or, another way to look at it is, before the MIN value of caln.clndr_dt or after the MAX value of caln.clndr_dt).
My goal is to be able to use the function in a situation like the following:
First, here's a sample table and data:
CREATE TABLE orders
(     ord_no          NUMBER(5),
     plan_start_dt     DATE,
     CONSTRAINT orders_pk PRIMARY KEY (ord_no)
INSERT INTO orders
VALUES (1,To_Date('01/08/1980','mm/dd/yyyy'));
INSERT INTO orders
VALUES (2,To_Date('01/09/1980','mm/dd/yyyy'));
INSERT INTO orders
VALUES (3,To_Date('01/10/1980','mm/dd/yyyy'));And here is how I would like to use my function:
SELECT     orders.ord_no
,     orders.plan_start_dt
,     add_mdays(orders.plan_start_dt, -3) AS prep_date
FROM     ordersThus, the function would allow me to return, for every order in my orders table, the date that is 3 workdays (mdays) prior to the plan start date of each order.
Am I going about this the right way? Do I need to create a function to do this, or is there a way for me to incorporate my query (that does my mday calculation) into the sample query above (eliminating the need to create a function)?
Thanks much in advance!
Edited by: user11033437 on Feb 2, 2010 8:55 AM
Fixed a couple typos in the last insert statements
Edited by: user11033437 on Feb 2, 2010 9:31 AM (fixed some syntax in the function)

Answer 1

Hi,
Ah, mentioning Oracle 8 and not being able to test your own code makes me nostalgic for the good old days, when you typed your cards, and brought them to a window at the computer center, and waited an hour for the job to run, and then saw the printout to find that you had made a typo.
If you're going to write functions, you really need to test them yourself. Like all code, functions whould be written in baby steps: write a line or two (or sometimes just part of what will later become one line), test, make sure it's running correctly, and repeat.
Ideally, your employer should create a developement schema in a development database for you to use.
You can legally download your own instance of Oracle Express Edition for free; just be careful not to use features that aren't available in the database where the code will be deployed.
You don't need a function to get the results you want:
SELECT       o.ord_no
,       o.plan_start_dt
,       MIN (e.clndr_dt)     AS prep_date
FROM       orders     o
,       caln          l
,       caln          e
WHERE       l.clndr_dt     = o.plan_start_dt
AND       e.shop_days     = l.shop_days - 3
GROUP BY  o.ord_no
,            o.plan_start_dt
;This would be more efficient (and a little simpler) if you added a column (let's call it work_day) that identified if each row represented a work_day or not.
For each value of shop_days, exactly 1 row will be marked as a work day.
Then the query might be something like:
SELECT       o.ord_no
,       o.plan_start_dt
,       e.clndr_dt          AS prep_date
FROM       orders     o
,       caln          l
,       caln          e
WHERE       l.clndr_dt     = o.plan_start_dt
AND       e.shop_days     = l.shop_days - 3
AND       e.work_day     = 1
;You could use the analytic LAG function to populate the work_day column.
A function would certainly be handy, though perhaps slower.
The function you posted has a few mistakes:
(a) An argument can't be declared as NUMBER (5); just NUMBER.
(b) When you SELECT in PL/SQL, like you're doing, you have to SELECT INTO some variable to hold the results.
(c) ROWNUM is arbitrary (which makes it useless in this problem) unless you are drawing from an ordered sub-query. I don't think you can use ORDER BY in sub-queries in Oracle 8. Use the analytic ROW_NUMBER function instead.
(d) The function must end with an END statement.
Given your current caln table, here's how I would write the function:
CREATE OR REPLACE FUNCTION add_mdays
     ( start_date     IN           DATE          DEFAULT     SYSDATE,
       mdays          IN           NUMBER          DEFAULT     1
RETURN     DATE
DETERMINISTIC
IS
     --     add_mdays returns the DATE that is mdays working days
     --     after start_date.  (If mdays < 0, the DATE returned
     --     will be before start_date).
     --     Work days do not include Saturdays, Sundays or holidays
     --     as indicated in the caln table.
     new_date     DATE;          -- to be returned
BEGIN
     SELECT     MIN (t.clndr_dt)
     INTO     new_date
     FROM     caln     f     -- f stands for "from"
     ,     caln     t     -- t stands for "to"
     WHERE     f.clndr_dt     = TRUNC (start_date)
     AND     t.shop_days     = f.shop_days + TRUNC (mdays)
     RETURN     new_date;
END     add_mdays;
SHOW ERRORSProduction code whould be robust (that includes "idiot-proofing").
Try to foresee what errors people might make in calling your function, and correct for them when possible.
For example, if it only makes sense for start_date to be midnight, or mdays to be an integer, then use TRUNC in the function in case soembody passes a bad value.
Allow for default arguments.
Comment your function. Put all comments within the function (that is, after CREATE and before the final END) so that they will be kept in the data dictionary.
If, given the same arguments, the function always returns the same value, mark it as DETERMINISTIC, for efficiency. This means the system may remember values passed back rather than call the function every time it is told to.
I wish I could mark questions as "Correct" or "Helpful"; you'd get 10 points for sure.
You posted CREATE TABLE and INSERT statements (without even being begged).
You gave a clear description of the problem, including desired results.
The code is nicely formatted and easy to read.
All around, one of the most thoughtful, well-written questions I've seen.
Well done! Keep up the good work!
Edited by: Frank Kulash on Feb 2, 2010 1:10 PM
Added my own version of the function.