ORACLE and TRIGGERS (inserted, updated, deleted)

From Using Triggers:

Detecting the DML Operation That Fired a Trigger

If more than one type of DML operation can fire a trigger (for example, ON INSERT OR DELETE OR UPDATE OF Emp_tab), the trigger body can use the conditional predicates INSERTING, DELETING, and UPDATING to check which type of statement fire the trigger.

So

IF DELETING THEN ... END IF;

should work for your case.

I've changed my code like this and it works:

CREATE or REPLACE TRIGGER test001  AFTER INSERT OR UPDATE OR DELETE ON tabletest001  REFERENCING OLD AS old_buffer NEW AS new_buffer   FOR EACH ROW WHEN (new_buffer.field1 = 'HBP00' OR old_buffer.field1 = 'HBP00') DECLARE      Operation       NUMBER;      CustomerCode    CHAR(10 BYTE);BEGINIF DELETING THEN   Operation := 3;  CustomerCode := :old_buffer.field1;END IF;IF INSERTING THEN   Operation := 1;  CustomerCode := :new_buffer.field1;END IF;IF UPDATING THEN   Operation := 2;  CustomerCode := :new_buffer.field1;END IF;    // DO SOMETHING ...EXCEPTION    WHEN OTHERS THEN ErrorCode := SQLCODE;END;

The NEW values (or NEW_BUFFER as you have renamed them) are only available when INSERTING and UPDATING. For DELETING you would need to use OLD (OLD_BUFFER). So your trigger would become:

CREATE or REPLACE TRIGGER test001  AFTER INSERT OR DELETE OR UPDATE ON tabletest001  REFERENCING OLD AS old_buffer NEW AS new_buffer   FOR EACH ROW WHEN (new_buffer.field1 = 'HBP00' OR old_buffer.field1 = 'HBP00') 

You may need to add logic inside the trigger to cater for code that updates field1 from 'HBP000' to something else.