Update only non empty fields

Question

Hi everybody,
I'm trying to develop a trigger-based solution for a project involving received messages from an MQ queue.
The messages are all inserted from the queue into a single staging table. (v10.2.0.4)
Each message's data will need to be either inserted or updated to a destination table based upon a field's value in the staging table.
I was planning on putting a trigger on the staging table and calling an insert or update procedure based on the staging field's value.
The inserts are pretty straightforward.
It's the updates that I'm struggling with - some of the staging fields will be populated, others will be empty. There is no pattern to which fields will or will not be populated.
I do not want to update the destination table with empty fields - I only want to update fields that contain data.
Is there an better way than several "if-then check for empty, then update" (one for each field)?
Maybe some sort of magical dynamic update?
Any help is greatly appreciated.
Thanks in advance!

Answer 1

Hi,
You can use the NVL function (or COALESCE), which returns the first of its arguments that is NOT NULL.
Instead of:
UPDATE  dest
SET     column_a = x
,       column_b = y
WHERE   id = z;say
UPDATE  dest
SET     column_a = NVL (x, column_a)
,       column_b = NVL (y, column_b)
WHERE   id = z;If x IS NOT NULL, then NVL (x, column_a) will return x.
If x IS NULL, then NVL (x, column_a) will return column_a
You could also automate this in a BEFORE UPDATE trigger:
:NEW.column_a := NVL (:NEW.column_a, :OLD.column_a);
:NEW.column_b := NVL (:NEW.column_a, :OLD.column_b);but if you do, you'll have to disable the trigger to correct mistakes that really should be NULL.