Before Update Trigger has mutating problem

Question

I'm getting a mutating problem with this updating trigger. I'm not sure how to deal with it. Here is my code:
CREATE OR REPLACE TRIGGER WTL_SMP_TRG2
BEFORE UPDATE ON WTL_SAMPLES
FOR EACH ROW
DECLARE
     sampleCount NUMBER(1) := 0;
     dupLabSampleID NUMBER(8) := 0;
BEGIN
     SELECT COUNT(sample_ID)
     INTO sampleCount
     FROM wtl_samples
WHERE jb_job_id = :new.jb_job_id
AND lab_no = :new.lab_no
     AND sample_ID != :old.sample_ID;
     IF sampleCount > 0 THEN
     SELECT sample_ID
     INTO dupLabSampleID
     FROM wtl_samples
     WHERE jb_job_id = :new.jb_job_id
     AND lab_no = :new.lab_no
          AND sample_ID != :old.sample_ID;
RAISE_APPLICATION_ERROR(-20501, 'Update failed, Lab Number ' || :new.lab_no || ' is used by SampleID: ' || dupLabSampleID);
END IF;
--EXCEPTION
--     WHEN OTHERS THEN
-- RAISE_APPLICATION_ERROR(-20901, 'Error in WTL_SMP_TRG2.');
END WTL_SMP_TRG2;
any help appreciated
adam

Answer 1

I guess I couldve done that, but was using design editor and didn't know how to put a unique constraint in. Is the problem only because I'm referencing the :old.sample_ID, or the :new values as well? If it's just the :old value I could write a before update statement trigger to place the sample_id into a package varaible and then call that variable up in the row level trigger.... i've tried this, but don't know how to pull the sample_id value i need in the before statement trigger... i'll supply the code i've done so far...
CREATE OR REPLACE TRIGGER WTL_SMP_TRG2_INIT
BEFORE UPDATE ON WTL_SAMPLES
DECLARE
BEGIN
     wtl_trg_custom_pkg.oldSampleID := sample_id; /* Doesn't know sample_id...? */
END WTL_SMP_TRG2_INIT;