DB2 Trigger: only update current row

1.

I notice in your trigger, your code says:

    INSERT INTO LYNX.TRANS_AUDIT
        (TA_ID, TA_KEY_VALUE, TA_TABLE_CHANGED, TA_FIELD_CHANGED, ...)
      VALUES 
        (TA_ID, N.UNIT_ID , 'PUNIT', 'FLEET_ID',  ...);

But shouldn't the VALUES clause contain vTA_ID instead?

    INSERT INTO LYNX.TRANS_AUDIT
        (TA_ID, TA_KEY_VALUE, TA_TABLE_CHANGED, TA_FIELD_CHANGED, ...)
      VALUES 
        (vTA_ID, N.UNIT_ID , 'PUNIT', 'FLEET_ID', ...);

However, calculating vTA_ID with your query, may not be your most efficient option.

2.

You could create a SEQUENCE object, and let it always calculate new values.

    CREATE SEQUENCE TRANS_AUDIT_SEQ AS INTEGER;

Then in your trigger,

    INSERT INTO LYNX.TRANS_AUDIT
        (TA_ID, TA_KEY_VALUE, TA_TABLE_CHANGED, TA_FIELD_CHANGED, ...)
      VALUES 
        (NEXT VALUE FOR TRANS_AUDIT_SEQ, N.UNIT_ID , 'PUNIT', 'FLEET_ID', ...);

3.

But what may suit you best, may be to define your ID column AS IDENTITY

CREATE TABLE LYNX.TRANS_AUDIT (
 TA_ID INTEGER  GENERATED BY DEFAULT AS IDENTITY,
    ...
 PRIMARY KEY (TA_ID)
);

Then in your trigger, you do not need to specify the value, since it will be generated for you:

    INSERT INTO LYNX.TRANS_AUDIT
        (TA_KEY_VALUE, TA_TABLE_CHANGED, TA_FIELD_CHANGED, ...)
      VALUES 
        (N.UNIT_ID , 'PUNIT', 'FLEET_ID',  ...);

This is most likely the best of the 3 solutions for you, unless there are other factors not mentioned.

Use the inserted table, which is a special table available inside triggers containing the rows that will be updated/inserted into the table.

ALTER TRIGGER tr_app_bread_crumbs_afterupdate
ON [dbo].[app_bread_crumbs]
AFTER UPDATE
AS
BEGIN 
    UPDATE [dbo].[app_bread_crumbs]
    SET last_updated_by = SYSTEM_USER,
    last_updated_on = GETDATE()
    FROM dbo.app_bread_crumbs abc
    WHERE EXISTS (SELECT 1 FROM inserted i WHERE i.id = abc.id);
END