Select previous max(date) and current max(date) in trigger

Question

Good mroning fellows!
I am trying to develop a row level trigger that inserts data into another table after insert.
Within the trigger I need to calculate a couple of averages based on dates. Therefore I need to select the date of the previously entered record and calculate the days between this last record and the current entry that was just saved.
Is it possible to write it like that in the trigger?
create or replace
TRIGGER borki.set_tageswerte
  AFTER INSERT
  ON borki.fangzahlen
  FOR EACH ROW
-- WHEN (NEW.qb_nr > 0 AND NEW.lrt_fl_id > 0) 
DECLARE
old_date        date;
latest_date     date;
days            number;
avergae_amount  integer;
BEGIN
old_date := (SELECT max(:old.date_datum)
     FROM borki.fangzahlen
     WHERE lng_falle = :new.lng_falle
     AND int_fallennummer = :new.int_fallennummer
     AND lng_schaedling = :new.lng_schaedling);
latest_date :=  (SELECT max(:new.date_datum)
     FROM borki.fangzahlen
     WHERE lng_falle = :new.lng_falle
     AND int_fallennummer = :new.int_fallennummer
     AND lng_schaedling = :new.lng_schaedling);
days := latest_date - old_date;
average_amount := (SELECT CASE
                   WHEN f.int_volumen > 0 AND f.lng_schaedling = 1 THEN f.int_volumen * 40
                   WHEN f.int_volumen > 0 AND f.lng_schaedling = 2 THEN f.int_volumen * 550
                   WHEN f.int_anzahl > 0 THEN f.int_anzahl
                   END
             / days AS tagesfang
        FROM borki.fangzahlen f
        WHERE f.lng_falle = :new.lng_falle
         AND f.int_fallennummer = :new.int_fallennummer
         AND f.lng_schaedling = :new.lng_schaedling
         AND days > 0
         AND ((f.int_anzahl > 0) OR (f.int_volumen > 0)))
     INSERT
         INTO fangzahlen_tageswerte
          lng_falle, date_datum, int_fallennummer, lng_schaedling, int_volumen, int_anzahl, lng_fangzahlen
        VALUES
        (SELECT f.lng_falle,
                   :new.date_datum, :new.int_fallennummer,
                   :new.lng_schaedling, :new.int_volumen,
                   :new.int_anzahl - ((y-1)*rec.tagesfang),
                   :new.objectid
END;thanks for sharing your wisdom mith me! :-)
Sebastian
Edited by: skahlert on 07.04.2010 07:04

Answer 1

Hello Tubby!
You're correct!
I'll take the time and show you what I got and what I need!
I am working with an Apex frontend where users enter scientific data for beetle monitoring.
The data entered consists of --> date_datum: date when last trap was emptied
--> int_volumen: the volume of the trap (used to calculate found specimen when int_anzahl is null)
--> int_anzahl: amount of found beetles
--> lng_schaedling: type of beetle (1 or 2)
--> lng_falle:trap number
--> int_fallennummer: sub-trap type (1 or 2)
Background info: Data is entered once or twice a week for each trap. After the data has been entered I need to calculate the mean average depending on the volume or amount.
Therefore I need to sum the colume or amount and divide it by the period of days since the current and last trap removal (that's when the bugs are counted and data is manually entered to the DB). For each day between the last and current trap removal I need to add one record in table fangzahlen_tageswerte (in my proc still called "test" for obvious reasons) that contains the mean average value of found beetles.
I hope I could point out my demand without confusing you!
PS: my problem --> very little background info concerning the entomological monitoring of this beetle type ;-), limited pl/sql skills and the problem that I need to run this procedure for each new record only. If you could show me how to make sure that data is not stored in table fangzahlen_tageswerte multiple times, I could called it directly in APEX.
Otherwise I'd suggest to create a trigger that launches this procedure below and parses the :new.parameters into my pocedure.
Another problem: this might work for insert statements. However, obviously I have to correct the mean values if raw data in table fangzahlen has been updated. Should I call another procedure after update on tbl fangzahlen or integrate that part into the procedure below? Doesn't matter I guess, right?
create or replace
PROCEDURE             "PR_FANGZAHLEN_TW_SK" (
   pr_falle          NUMBER,
   pr_fallennummer   NUMBER,
   pr_schaedling     NUMBER
IS
   old_date                  DATE;
   diff_days                 NUMBER (10);
   tagesfang                 NUMBER (12);
   y                         NUMBER (10);
BEGIN
   /*Query date of previous record and store it into variable old_date*/
    select date_datum into old_date from
    (select f.date_datum, row_number() over (order by f.date_datum desc) rn
    from borki.fangzahlen f where f.lng_falle = pr_falle
    and f.int_fallennummer = pr_fallennummer
    and f.lng_schaedling = pr_schaedling) where rn=2;
    select max(f.date_datum) - old_date into diff_days from borki.fangzahlen f
     where (f.lng_falle = pr_falle)
     and (f.int_fallennummer = pr_fallennummer)
     and (f.lng_schaedling = pr_schaedling);
   FOR rec IN (select sum((case
                   when f.int_volumen > 0 and f.lng_schaedling = 1
                      then f.int_volumen * 40
                   when f.int_volumen > 0 and f.lng_schaedling = 2
                      then f.int_volumen * 550
                   when f.int_anzahl > 0
                      then f.int_anzahl
                end
             / (f.date_datum - to_date(old_date))) as tagesfang
        from borki.fangzahlen f
        where (f.lng_falle = pr_falle)
         and (f.int_fallennummer = pr_fallennummer)
         and (f.lng_schaedling = pr_schaedling)
         and ((f.date_datum - to_date(old_date)) > 0)
         and ((f.int_anzahl > 0) or (f.int_volumen > 0))) 
      LOOP
            y := 1;
      WHILE y < diff_days + 1
      LOOP
      /* Insert FANGZAHLEN_TAGESWERTE*/
       IF  y < diff_days
       THEN
         INSERT INTO test
                     (lng_falle, date_datum, int_fallennummer,
                      lng_schaedling, int_volumen, int_anzahl,
                      lng_fangzahlen)
            SELECT f.lng_falle,
                   old_date + y, f.int_fallennummer,
                   f.lng_schaedling, f.int_volumen, rec.tagesfang,
                   f.objectid
              FROM fangzahlen f
             WHERE     f.lng_falle = pr_falle
                   AND f.int_fallennummer = pr_fallennummer
                   AND f.lng_schaedling = pr_schaedling
                   AND (f.date_datum - old_date) > 0
                   AND ( (f.int_anzahl > 0)
                OR (f.int_volumen > 0) );
       END IF;
         y := y + 1;
      END LOOP;
END LOOP; -- end of cursor
EXCEPTION
   WHEN NO_DATA_FOUND
   THEN
      NULL;
   WHEN OTHERS
   THEN
      -- Consider logging the error and then re-raise
      RAISE;
END "PR_FANGZAHLEN_TW_SK";regards,
Seb