Trigger function to know which fields are being updated

I am writing a trigger function. How can I know which fields are being 
updated in the PL/SQL function?

For example I have a table here:


CREATE TABLE COMPANY ( COMPANY_ID VARCHAR(10) NOT NULL, NAME VARCHAR(30), ADDRESS VARCHAR(30));

I want to write a trigger to block all update statements without updating 
NAME. I tried the following code block and it doesn't work:

 IF TG_OP = ''UPDATE'' THEN    IF NEW.NAME IS NULL THEN       RAISE NOTICE ''Field NAME must be provided!'';    END IF;
ENDIF;
 

Are there any functions like the Oracle's UPDATING() predicate?

Bernard Cheung

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